Pet-imaging immunomodulators

ABSTRACT

The invention relates to the synthesis and use of  18 F-labeled millamolecules for imaging various processes within the body, for detecting the location of molecules associated with disease pathology, and for monitoring disease progression are disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/338,872 filed May 19, 2016, which is incorporated byreference in its entirety.

The present disclosure generally relates to immunomodulators containing¹⁸F-prosthetic groups and the synthesis and use of ¹⁸F-labeledimmunomodulators for imaging various processes within the body, fordetecting the location of molecules associated with disease pathology,and for monitoring disease progression.

Positron emission tomography (PET) is a non-invasive imaging techniquethat has become one of the most widely used methods in diagnosticmedicine and drug development, with high sensitivity (fmoles), highresolution (4-10 mm) and tissue accretion that can be quantitated. Thevaluable in vivo functional information about biological processes inliving subjects provided by PET imaging also provides a uniquetranslational medical advantage in that the same tool can be used bothpreclinically and clinically.

PET relies on the design and synthesis of molecules labeled with apositron-emitting radioisotopes including ¹⁸F, ₆₄Cu, ¹¹C, ¹⁵ 0, ¹³N,⁶⁶Ga, ⁶⁸Ga, ⁷⁶Br, ⁸⁹Zr, ⁹⁴mTc, ⁸⁶Y and ¹²⁴I. In vivo, these radiotracersor radioligands emit positrons from the nucleus of the isotope withdifferent energies depending on the isotope used. The energy of theejected positron controls the average distance that it travels before itcollides with an electron resulting in the emission of two 511 keV gammarays in opposite directions. The gamma rays produced by this positronannihilation event are detected by the PET imaging scanner to produceplanar and tomographic images that reveal distribution of theradiotracer as a function of time. Accordingly, isotopes that are purepositron emitters with low ejection energy isotopes are preferred forPET imaging to minimize the distance traveled by the positron beforeannihilation and dosimetry problems caused by other emissions such asgamma rays, alpha particles or beta particles.

In addition, the half-life of the isotope used in PET imaging must belong enough to allow synthesis and analysis of the radiotracer molecule,injection into the patient, in vivo localization, clearance fromnon-target tissues, and the production of a clear image. ¹⁸F (β⁺635 keV97%, t_(1/2) 110 min) is one of the most widely used PET emittingisotopes because of its low positron emission energy, lack of sideemissions and suitable half-life.

The present disclosure relates to a millamolecule substituted with an¹⁸F-labeled prosthetic group that contains a nitro-pyridine linked to apolyethylene glycol (PEG) moiety and a terminal azide. In certainembodiments, millamolecules containing bifunctional conjugating moieties(e.g., with ring constrained alkyne groups) form covalent bonds with theterminal azide of the ¹⁸F-labeled prosthetic group via a “click”biorthogonal reaction to produce radiolabeled probes that are stableunder physiological conditions. The UV absorbance of the resultantproduct further provides a practical, sensitive and rapid analyticalmethod for determining the radiochemical purity of the product. These18F labelled millamolecules are useful for detecting the presence ofPD-L1 in cells and tissues such as tumors which can provide valuabletreatment information.

Other features and advantages of the present disclosure will be apparentfrom the following detailed description and examples, which should notbe construed as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representative PET/CT images of [¹⁸F]labelled macrocyclicPD-L1 peptide in mice bearing bilateral PD-L1 (+) L2987 and PD-L1 (−)xenograft tumors.

FIG. 2 shows averaged time-activity curves for [¹⁸F]labelled macrocyclicPD-L1 peptide radiotracers.

FIG. 3 is a representative PET images of [¹⁸F]labelled macrocyclic PD-L1peptide radiotracer in non-human primate.

FIG. 4 shows autoradiogram images of [¹⁸F]labelled macrocyclic PD-L1peptide radiotracer in xenograft (A &B) and human non-small cell lungcancer biopsied tissues (C &D).

In its first aspect the present disclosure provides a compound offormula (I)

or a pharmaceutically acceptable salt thereof, wherein x is an integerfrom 1 to 8 and R is a C₁-C₆ alkyl group.

In a second aspect the present disclosure provides a compound of formula(II)

or a pharmaceutically acceptable salt thereof, wherein x is an integerfrom 1 to 8 and R is C₁-C₆ alkyl group.

In a third aspect the present disclosure provides a compound of formula(III)

or a pharmaceutically acceptable salt thereof.

In a fourth aspect the present disclosure provides a compound of formula(IV)

or a pharmaceutically acceptable salt thereof, wherein x is an integerfrom 1 to 8 and R is C₁-C₆ alkyl group.

In a fifth aspect the present disclosure provides a compound of formula(V)

or a pharmaceutically acceptable salt thereof.

In a sixth aspect the present disclosure provides a method of obtainingan image of a compound of formula (I)-(V), or a pharmaceuticallyacceptable salt thereof, the method comprising,

a) administering the compound to a subject; and

b) imaging in vivo the distribution of compound by positron emissiontomography (PET) scanning.

In a first embodiment of the sixth aspect the imaged distribution of thecompound of formula (I)-(V), or a pharmaceutically acceptable saltthereof, is indicative of the presence or absence of a disease.

In a seventh aspect the present disclosure provides a method ofmonitoring the progress of a disease in a subject, the method comprising

(a) administering to a subject in need thereof a compound of formula(I)-(V), or a pharmaceutically acceptable salt thereof, which binds to atarget molecule associated with the presence of the disease at a firsttime point and obtaining an image of at least a portion of the subjectto determine the amount of the diseased cells or tissue; and

(b) administering to the subject compound at one or more subsequent timepoints and obtaining an image of at least a portion of the subject ateach time point; wherein the dimension and location of the diseasedcells or tissue at each time point is indicative of the progress of thedisease.

In an eighth aspect the present disclosure provides a method ofquantifying diseased cells or tissues in a subject, the methodcomprising

(a) administering to a subject having diseased cells or tissues acompound of formula (I)-(V) or a pharmaceutically acceptable saltthereof which binds to a target molecule located with the diseased cellsor tissues; and

(b) detecting radioactive emissions of the ¹⁸F in the diseased cells ortissue, wherein the level and distribution of the radioactive emissionsin the diseased cells or tissues is a quantitative measure of thediseased cells or tissues.

In a first embodiment of the eighth aspect the disease is selected fromthe group consisting of solid cancers, hematopoietic cancers,hematological cancers, autoimmune disease, neurodegenerative diseasecardiovascular disease, and pathogenic infection.

In a ninth aspect the present disclosure provides a method of obtaininga quantitative image of tissues or cells expressing PD-L1, the methodcomprising contacting the cells or tissue with a compound of formula(I)-(V) or a pharmaceutically acceptable salt thereof which binds toPD-L1, and detecting or quantifying the tissue expressing PD-L1 usingpositron emission tomography (PET).

In a tenth aspect the present disclosure provides a method of screeningfor an agent for treating a disease comprising the steps of

(a) contacting cells expressing PD-L1 with a compound of formula (I)-(V)or a pharmaceutically acceptable salt thereof which binds to PD-L1 inthe presence and absence of a candidate agent; and

(b) imaging the cells in the presence and absence of the candidate agentusing positron emission tomography (PET),

wherein a decrease in the amount of radioactive emissions in thepresence of the candidate agent is indicative of that the agent binds toPD-L1.

In an eleventh aspect the present disclosure provides a diagnostic agentor a pharmaceutical composition comprising a compound of formula (I) ora pharmaceutically acceptable salt thereof.

In a twelfth aspect the present disclosure provides a kit comprising thereaction precursors for use in producing the compound of formula (I),and instructions for producing the compound of formula (I) or apharmaceutically acceptable salt thereof

In another aspect, the present disclosure provides a compound accordingto formula (I)-(V) or a pharmaceutically acceptable salt thereof for useas an imaging agent.

In another aspect, the present disclosure provides a compound accordingto formula (I)-(V) or a pharmaceutically acceptable salt thereof for usein diagnosing a disease in a subject. Typically, the diagnosis includesthe detection or monitoring of the progress of a disease in a subject.According to one embodiment, the compound according to formula (I)-(V)is administered to the subject requiring the diagnosis and directvisualization of the diseased cells and tissues is carried out usingpositron emission tomography.

In another aspect, the present disclosure provides a method ofdiagnosing ex-vivo a disease in a subject which is related to the leveland distribution in tissues and cells of PD-L1 expression using acompound of formula (I)-(V) or a pharmaceutically acceptable saltthereof

In another aspect, the present disclosure provides a method ofmonitoring in-vitro the progress of a disease in a subject, the methodcomprising:

(a) at a first time point; contacting a sample of cells or tissues ofone subject with a compound of formula (I)-(V) wherein the compoundbinds to a target molecule associated with the presence of the diseaseand obtaining an image using positron emission tomography; and

(b) at one or more subsequent time points, contacting another sample ofcells or tissues with a compound of formula (I)-(V) and obtaining animage at each time point;

wherein the dimension and location of the diseased cells or tissue ateach time point is indicative of the progress of the disease.

In another aspect, the present disclosure provides a method ofquantifying in-vitro diseased cells or tissues in a subject, the methodscomprising:

(a) contacting a sample of cells or tissues of one subject with acompound of formula (I)-(V) wherein the compound binds to a targetmolecule associated with the presence of the disease and obtaining animage using positron emission tomography; and

(b) detecting radioactive emissions of the ¹⁸F in the diseased cells ortissue, wherein the level and distribution of the radioactive emissionsin the diseased cells or tissues is a quantitative measure of thediseased cells or tissues.

According to one embodiment of any of the aspects of the presentdisclosure, the disease is related to the level and distribution intissues and cells expressing PD-L1.

Typically, the disease is selected from the group consisting of solidcancers, hematopoietic cancers, hematological cancers, autoimmunediseases, neurodegenerative disease, cardiovascular disease andpathogenic diseases. In another embodiment, the disease is solidcancers.

According to another aspect, the present disclosure provides a methodfor preparing the compound according to formula (I)-(V).

Described herein are ¹⁸F-prosthetic groups and methods for producing the¹⁸F-prosthetic groups. Also described herein are radiolabeledcompositions containing the ¹⁸F-prosthetic groups and the use of theseradiolabeled compositions to diagnose, localize, monitor and/or assessdiseased cells and/or tissues, and related biological conditions.

In order that the present description may be more readily understood,certain terms are first defined. Additional definitions are set forththroughout the detailed description. Unless defined otherwise, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art, andconventional methods of mass spectroscopy, NMR, HPLC, biochemistry,recombinant DNA techniques and pharmacology are employed.

As used herein, the singular forms “a”, “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The use of “or”or “and” means “and/or” unless stated otherwise. Furthermore, use of theterm “including” as well as other forms, such as “include”, “includes”,and “included”, is not limiting.

As used herein, “about” means within plus or minus ten percent of anumber. For example, “about 100” would refer to any number between 90and 110.

As used herein, “medical imaging” refers to the techniques and processesused to create images of the subject's body (or parts thereof) forclinical purposes (medical procedures seeking to reveal, diagnose ormonitor disease) or medical science (including the study of normalanatomy and physiology).

As used herein, “positron emission tomography” or “PET” refers to anon-invasive, nuclear medicine technique that produces athree-dimensional image of tracer location in the body. The methoddetects pairs of gamma rays emitted indirectly by a positron-emittingradionuclide (tracer), which is introduced into the body on abiologically active molecule. PET imaging tools have a wide variety ofuses and aid in drug development both preclinically and clinically.Exemplary applications include direct visualization of in vivosaturation of targets; monitoring uptake in normal tissues to anticipatetoxicity or patient to patient variation; quantifying diseased tissue;tumor metastasis; and monitoring drug efficacy over time, or resistanceover time.

The term “bioorthogonal chemistry” refers to any chemical reaction thatcan occur inside of living systems without interfering with nativebiochemical processes. The term includes chemical reactions that arechemical reactions that occur in vitro at physiological pH in, or in thepresence of water. To be considered bioorthogonol, the reactions areselective and avoid side-reactions with other functional groups found inthe starting compounds. In addition, the resulting covalent bond betweenthe reaction partners should be strong and chemically inert tobiological reactions and should not affect the biological activity ofthe desired molecule.

The term “click chemistry” refers to a set of reliable and selectivebioorthogonal reactions for the rapid synthesis of new compounds andcombinatorial libraries. Properties of for click reactions includemodularity, wideness in scope, high yielding, stereospecificity andsimple product isolation (separation from inert by-products bynon-chromatographic methods) to produce compounds that are stable underphysiological conditions. In radiochemistry and radiopharmacy, clickchemisty is a generic term for a set of labeling reactions which makeuse of selective and modular building blocks and enable chemoselectiveligations to radiolabel biologically relevant compounds in the absenceof catalysts. A “click reaction” can be with copper, or it can be acopper-free click reaction.

The term “prosthetic group” or “bifunctional labeling agent” refers to asmall organic molecule containing a radionuclide (e.g., ¹⁸F) that iscapable of being linked to a millamolecule.

As used herein, “target” as a general reference to a “biological target”refers to a cell, tissue (e.g., cancer or tumor), a pathogenicmicroorganism (e.g., bacteria, virus, fungus, plant, prion, protozoa orportion thereof) or other molecule associated with a biological pathway,or a biological phenomenon, such as tissue inflammation, plaqueformation, etc.

The term “targeting ligand”, “targeting agent” or “targeting molecule”are used interchangeably to refer to a molecule, such as a peptide,millamolecule, etc., that binds to another molecule. In certainembodiments, a targeting agent is bound to the ¹⁸F-prosthetic group inorder to “target” a molecule associated with a particular cell, tissue,pathogen or biological pathway.

The terms “specifically binds,” “specific binding,” “selective binding,and “selectively binds,” as used interchangeably herein refers to anpeptide or polypeptide that exhibits affinity for a biological target,but does not significantly bind (e.g., less than about 10% binding) to aother molecules as measured by a technique available in the art such as,but not limited to, Scatchard analysis and/or competitive binding assays(e.g., competition ELISA, BIACORE assay).

The term “IC₅₀”, as used herein, refers to the concentration of an¹⁸F-radiolabeled-millamolecule based probe that inhibits a response,either in an in vitro or an in vivo assay, to a level that is 50% of themaximal inhibitory response, i.e., halfway between the maximalinhibitory response and the untreated response.

As used herein, the term “linked” refers to the association of two ormore molecules. The linkage can be covalent or non-covalent.

The terms “diagnosis” or “detection” can be used interchangeably.Whereas diagnosis usually refers to defining a tissue's specifichistological status, detection recognizes and locates a tissue, lesionor organism containing a particular detectable target.

The term “detectable” refers to the ability to detect a signal over thebackground signal. The term “detectable signal” as used herein in thecontext of imaging agents and diagnostics, is a signal derived fromnon-invasive imaging techniques such as, but not limited to, positronemission tomography (PET). The detectable signal is detectable anddistinguishable from other background signals that may be generated fromthe subject. In other words, there is a measurable and statisticallysignificant difference (e.g., a statistically significant difference isenough of a difference to distinguish among the detectable signal andthe background, such as about 0.1%, 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%,or 40% or more difference between the detectable signal and thebackground) between the detectable signal and the background. Standardsand/or calibration curves can be used to determine the relativeintensity of the detectable signal and/or the background.

A “detectably effective amount” of a composition comprising an imagingagent described herein is defined as an amount sufficient to yield anacceptable image using equipment that is available for clinical use. Adetectably effective amount of an imaging agent provided herein may beadministered in more than one injection. The detectably effective amountcan vary according to factors such as the degree of susceptibility ofthe individual, the age, sex, and weight of the individual,idiosyncratic responses of the individual, and the like. Detectablyeffective amounts of imaging compositions can also vary according toinstrument and methodologies used. Optimization of such factors is wellwithin the level of skill in the art.

As used herein, “administering,” as used in the context of imagingagents refers to the physical introduction of a composition comprisingan imaging agent to a subject, using any of the various methods anddelivery systems known to those skilled in the art. Preferred routes ofadministration for the imaging agents described herein includeintravenous, intraperitoneal, intramuscular, subcutaneous, spinal orother parenteral routes of administration, for example by injection orinfusion. The phrase “parenteral administration” as used herein meansmodes of administration other than enteral and topical administration,usually by injection, and includes, without limitation, intravenous,intraperitoneal, intramuscular, intraarterial, intrathecal,intralymphatic, intralesional, intracapsular, intraorbital,intracardiac, intradermal, transtracheal, subcutaneous, subcuticular,intraarticular, subcapsular, subarachnoid, intraspinal, epidural andintrasternal injection and infusion, as well as in vivo electroporation.Alternatively, an imaging agent described herein can be administered viaa non-parenteral route, such as a topical, epidermal or mucosal route ofadministration, for example, intranasally, orally, vaginally, rectally,sublingually or topically. Administering can also be performed, forexample, once, a plurality of times, and/or over one or more extendedperiods.

The terms “co-administration” or the like, as used herein, are meant toencompass administration of the selected pharmaceutical agents to asingle patient, and are intended to include regimens in which the agentsare administered by the same or different route of administration or atthe same or different time.

The terms “patient” and “subject” refer to any human or non-human animalthat receives a composition comprising an imaging agent describedherein. For in vitro applications, such as in vitro diagnostic andresearch applications, body fluids and cell samples of the abovesubjects will be suitable for use, such as blood, urine, or tissuesamples.

The term “sample” can refer to a tissue sample, cell sample, a fluidsample, and the like. The sample may be taken from a subject. The tissuesample can include hair (including roots), buccal swabs, blood, saliva,semen, muscle, or from any internal organs. The fluid may be, but is notlimited to, urine, blood, ascites, pleural fluid, spinal fluid, and thelike. The body tissue can include, but is not limited to, skin, muscle,endometrial, uterine, and cervical tissue.

The term “isotopically pure” means that the element, compound, orcomposition contains a greater proportion of one isotope in relation toother isotopes. In certain embodiments, the element, compound, orcomposition is greater than about 40%, 50%, or 60% isotopically pure.

As used herein, a labeled molecule is “purified” when the labeledmolecule is partially or wholly separated from unlabeled molecules, sothat the fraction of labeled molecules is enriched compared to thestarting mixture. A “purified” labeled molecule may comprise a mixtureof labeled and unlabeled molecules in almost any ratio, including butnot limited to about 5:95; 10:90; 15:85; 20:80; 25:75; 30:70; 40:60;50:50; 60:40; 70:30; 75:25; 80:20; 85:15; 90:10; 95:5; 97:3; 98:2; 99:1or 100:0.

The group “OTf” refers to triflate having the formula CF₃SO₃ ortrifluoromethanesulfate.

The term “halo” or, alternatively, “halogen” or “halide” means fluoro,chloro, bromo or iodo.

Throughout the specification, groups and substituents thereof may bechosen by one skilled in the field to provide stable moieties andcompounds and compounds useful as pharmaceutically-acceptable compoundsand/or intermediate compounds useful in makingpharmaceutically-acceptable compounds.

Various aspects described herein are described in further detail in thefollowing subsections.

¹⁸F Radiolabeled Prosthetic Groups

In one aspect, provided herein is a PEGylated ¹⁸F-pyridine covalentlybound to an azide with the following structure,

or a pharmaceutically acceptable salt thereof, wherein x is an integerfrom 1 to 8. In some embodiments, x is an integer from 2 to 6. In someembodiments x is an integer from 3 to 5. In some embodiments, x is 4. Inrelated embodiments, ¹⁸F is attached to the pyridine ortho to the Natom. In some embodiments, the [O(CH₂)₂]_(x) moiety is present in the1-3 configuration relative to the nitrogen on the pyridine ring. In someembodiments, the [O(CH₂)₂]_(x) moiety is present in the 1-2configuration relative to the nitrogen on the pyridine ring. In otherembodiments, the [O(CH₂)₂]_(x) moiety is present in the 1-4configuration relative to the nitrogen on the pyridine ring.

In some embodiments, the ¹⁸F-radiolabeled compound has the structure

or a pharmaceutically acceptable salt thereof, wherein x is an integerfrom 1 to 8. In some embodiments, x is an integer from 2 to 6. In someembodiments x is an integer from 3 to 5. In some embodiments, x is 4. Insome embodiments, the [O(CH₂)₂]_(x) moiety is present in the 1-3configuration relative to the nitrogen on the pyridine ring. In someembodiments, the [O(CH₂)₂]_(x) moiety is present in the 1-2configuration relative to the nitrogen on the pyridine ring. In otherembodiments, the [O(CH₂)₂]_(x) moiety is present in the 1-4configuration relative to the nitrogen on the pyridine ring.

In some embodiments, the ¹⁸F-radiolabeled compound has the structure

wherein x is an integer from 1 to 8. In some embodiments, x is aninteger from 2 to 6. In some embodiments x is an integer from 3 to 5. Insome embodiments, x is 4.

In some embodiments, the ¹⁸F-radiolabeled compound is[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine(¹⁸F-FPPEGA) and has the structure

In alternative embodiments, the ¹⁸F-radiolabeled prosthetic group maycontain additional groups on the pyridine ring which do not interferewith the fluorination reaction. In certain embodiments, additions to thepyridine ring include C₁₋₆ alkyl groups, for example methyl, ethyl andpropyl.

In still other embodiments, the ¹⁸F-radiolabeled prosthetic group is afused ring system with the following structure:

wherein “OPEG” is [O(CH₂)₂]_(x), and x is an integer from 1 to 8. Insome embodiments, x is an integer from 2 to 6. In some embodiments x isan integer from 3 to 5. In some embodiments, x is 4.

In a related aspect, provided herein is a method of preparing aPEGylated ¹⁸F-pyridine covalently bound to an azide with the followingstructure,

wherein x is an integer from 1 to 8, the method comprising the steps of(a) providing a solution of a compound a with the following structure:

wherein x is an integer from 1 to 8, and R is NO₂, Br, F or

and is ortho to the N atom of the pyridine ring;(b) providing a mixture of ¹⁸F in ¹⁸Owater,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane and a weakbase;(c) drying the mixture from step (b) to form a solid; and(d) reacting the solution from step (a) with the solid from step (c) toform the ¹⁸F-labeled compound.

In certain embodiments, the method produces a ¹⁸F-pyridine prostheticgroup with the following structure b

(where ¹⁸F is ortho to the N atom), and includes the steps of

(a) providing a solution of the compound of the structure

(where X is ortho to the N atom) where X is NO₂, Br or

(b) providing a mixture of ¹⁸F in ¹⁸Owater,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane and weakbase, such as K₂CO₃;

(c) drying the mixture from step (b) to form a solid; and

(d) reacting the solution from step (a) with the solid from step (c) toform the ¹⁸F-labeled compound.

In certain embodiments, the method further comprises the step ofproducing a compound with the following structure a

according to the Scheme I shown below:

In certain embodiments, the method comprises producing the ¹⁸F-pyridineprosthetic group[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine

(¹⁸F-FPPEGA), e, from d, according to the following reaction conditions:

Formulations

Further provided are compositions, e.g., a pharmaceutical compositions,containing one or a combination of ¹⁸F-labeled targeting agents,described herein, formulated together with a pharmaceutically acceptablecarrier. Such compositions may include one or a combination of (e.g.,two or more different) agents described herein. For example, apharmaceutical composition described herein can comprise a combinationof ¹⁸F-labeled targeting agent and a drug.

As used herein, “pharmaceutically acceptable carrier” includes any andall solvents, dispersion media, coatings, antibacterial and antifungalagents, isotonic and absorption delaying agents, and the like that arephysiologically compatible. Preferably, the carrier is suitable forintravenous, intramuscular, subcutaneous, parenteral, spinal orepidermal administration (e.g., by injection or infusion). Depending onthe route of administration, ¹⁸F-labeled targeting agent may be coatedin a material to protect the compound from the action of acids and othernatural conditions that may inactivate the compound.

The pharmaceutical compounds described herein may include one or morepharmaceutically acceptable salts. A “pharmaceutically acceptable salt”refers to a salt that retains the desired biological activity of theparent compound and does not impart any undesired toxicological effects(see e.g., Berge, S. M., et al. (1977) J. Pharm. Sci. 66:1-19). Examplesof such salts include acid addition salts and base addition salts. Acidaddition salts include those derived from nontoxic inorganic acids, suchas hydrochloric, nitric, phosphoric, sulfuric, hydrobromic, hydroiodic,phosphorous and the like, as well as from nontoxic organic acids such asaliphatic mono- and dicarboxylic acids, phenyl-substituted alkanoicacids, hydroxy alkanoic acids, aromatic acids, aliphatic and aromaticsulfonic acids and the like. Base addition salts include those derivedfrom alkaline earth metals, such as sodium, potassium, magnesium,calcium and the like, as well as from nontoxic organic amines, such asN,N′-dibenzylethylenediamine, N-methylglucamine, chloroprocaine,choline, diethanolamine, ethylenediamine, procaine and the like.

A pharmaceutical composition described herein also may include apharmaceutically acceptable anti-oxidant. Examples of pharmaceuticallyacceptable antioxidants include: (1) water soluble antioxidants, such asascorbic acid, cysteine hydrochloride, sodium bisulfate, sodiummetabisulfite, sodium sulfite and the like; (2) oil-solubleantioxidants, such as ascorbyl palmitate, butylated hydroxyanisole(BHA), butylated hydroxytoluene (BHT), lecithin, propyl gallate,alpha-tocopherol, and the like; and (3) metal chelating agents, such ascitric acid, ethylenediamine tetraacetic acid (EDTA), sorbitol, tartaricacid, phosphoric acid, and the like.

Examples of suitable aqueous and nonaqueous carriers that may beemployed in the pharmaceutical compositions described herein includewater, ethanol, polyols (such as glycerol, propylene glycol,polyethylene glycol, and the like), and suitable mixtures thereof,vegetable oils, such as olive oil, and injectable organic esters, suchas ethyl oleate. Proper fluidity can be maintained, for example, by theuse of coating materials, such as lecithin, by the maintenance of therequired particle size in the case of dispersions, and by the use ofsurfactants.

These compositions may also contain adjuvants such as preservatives,wetting agents, emulsifying agents and dispersing agents. Prevention ofpresence of microorganisms may be ensured both by sterilizationprocedures, supra, and by the inclusion of various antibacterial andantifungal agents, for example, paraben, chlorobutanol, phenol sorbicacid, and the like. It may also be desirable to include isotonic agents,such as sugars, sodium chloride, and the like into the compositions. Inaddition, prolonged absorption of the injectable pharmaceutical form maybe brought about by the inclusion of agents which delay absorption suchas aluminum monostearate and gelatin.

Pharmaceutically acceptable carriers include sterile aqueous solutionsor dispersions and sterile powders for the extemporaneous preparation ofsterile injectable solutions or dispersion. The use of such media andagents for pharmaceutically active substances is known in the art.Except insofar as any conventional media or agent is incompatible withthe active compound, use thereof in the pharmaceutical compositionsdescribed herein is contemplated. Supplementary active compounds canalso be incorporated into the compositions.

Pharmaceutical compositions typically must be sterile and stable underthe conditions of manufacture and storage. The composition can beformulated as a solution, microemulsion, liposome, or other orderedstructure suitable to high drug concentration. The carrier can be asolvent or dispersion medium containing, for example, water, ethanol,polyol (for example, glycerol, propylene glycol, and liquid polyethyleneglycol, and the like), and suitable mixtures thereof. The properfluidity can be maintained, for example, by the use of a coating such aslecithin, by the maintenance of the required particle size in the caseof dispersion and by the use of surfactants. In many cases, it will bepreferable to include isotonic agents, for example, sugars, polyalcoholssuch as mannitol, sorbitol, or sodium chloride in the composition.Prolonged absorption of the injectable compositions can be brought aboutby including in the composition an agent that delays absorption, forexample, monostearate salts and gelatin.

Sterile injectable solutions can be prepared by incorporating the¹⁸F-labeled targeting agent in the required amount in an appropriatesolvent with one or a combination of ingredients enumerated above, asrequired, followed by sterilization microfiltration. Generally,dispersions are prepared by incorporating the active compound into asterile vehicle that contains a basic dispersion medium and the requiredother ingredients from those enumerated above. In the case of sterilepowders for the preparation of sterile injectable solutions, thepreferred methods of preparation are vacuum drying and freeze-drying(lyophilization) that yield a powder of the active ingredient plus anyadditional desired ingredient from a previously sterile-filteredsolution thereof.

The amount of ¹⁸F-labeled targeting agent which can be combined with acarrier material to produce a single dosage form will vary dependingupon the subject being treated, and the particular mode ofadministration. The amount of ¹⁸F-labeled targeting agent which can becombined with a carrier material to produce a single dosage form willgenerally be that amount of the composition which produces a detectableeffect.

Generally, out of one hundred per cent, this amount will range fromabout 0.01 per cent to about ninety-nine percent of active ingredient,preferably from about 0.1 per cent to about 70 per cent, most preferablyfrom about 1 per cent to about 30 per cent of active ingredient incombination with a pharmaceutically acceptable carrier.

Administration and Imaging

The ¹⁸F-labeled targeting agents described herein are useful in avariety of in vivo imaging applications (e.g., for tissue or whole bodyimaging). In certain embodiments, the ¹⁸F-labeled targeting agent can beused to image target-positive cells or tissues, e.g., target expressingtumors. For example, the labeled ¹⁸F-labeled targeting agent isadministered to a subject in an amount sufficient to uptake the¹⁸F-labeled targeting agent into the tissue of interest. The subject isthen imaged using an imaging system such as PET for an amount of timeappropriate for the ¹⁸F radionuclide. The ¹⁸F-labeled targetingagent-bound to cells or tissues expressing the targeting agent are thendetected by the imaging system.

Typically, for imaging purposes it is desirable to provide the recipientwith a dosage of millamolecule that is in the range of from about 1 mgto 200 mg as a single intravenous infusion, although a lower or higherdosage also may be administered as circumstances dictate. Typically, itis desirable to provide the recipient with a dosage that is in the rangeof from about 1 mg to 10 mg per square meter of body surface area of theprotein or peptide for the typical adult, although a lower or higherdosage also may be administered as circumstances dictate. Examples ofdosages proteins or peptides that may be administered to a human subjectfor imaging purposes are about 1 to 200 mg, about 1 to 70 mg, about 1 to20 mg, and about 1 to 10 mg, although higher or lower doses may be used.

In certain embodiments, administration occurs in an amount of¹⁸F-radiolabeled-millamolecule of between about 0.005 μg/kg of bodyweight to about 50 μg/kg of body weight per day, usually between 0.02μg/kg of body weight to about 3 μg/kg of body weight. The massassociated with a PET tracer is in the form of the natural isotope,namely ¹⁹F for the ¹⁸F PET tracer. A particular analytical dosage forthe instant composition includes from about 0.5 μg to about 100 μg of an¹⁸F-radiolabeled millamolecule. The dosage will usually be from about 1μg to about 50 μg of an ¹⁸F-radiolabeled millamolecule.

Dosage regimens are adjusted to provide the optimum detectable amountfor obtaining a clear image of the tissue or cells which uptake the¹⁸F-labeled targeting agent. It is especially advantageous to formulateparenteral compositions in dosage unit form for ease of administrationand uniformity of dosage. Dosage unit form as used herein refers tophysically discrete units suited as unitary dosages for the subjects towhich the ¹⁸F-labeled targeting agent is to be administered. Thespecification for the dosage unit forms described herein are dictated byand directly dependent on (a) the unique characteristics of thetargeting portion of the ¹⁸F-labeled targeting agent; (b) the tissue orcells to be targeted; (c) the limitations inherent in the imagingtechnology used.

For administration of the ¹⁸F-labeled targeting agent, the dosage usedwill depend upon the disease type, targeting compound used, the age,physical condition, and gender of the subject, the degree of thedisease, the site to be examined, and others. In particular, sufficientcare has to be taken about exposure doses to a subject. Preferably, asaturating dose of ¹⁸⁻F is administered to the patient. For example, theamount of radioactivity of ¹⁸F-labeled targeting agent usually rangesfrom 3.7 megabecquerels to 3.7 gigabecquerels, and preferably from 18megabecquerels to 740 megabecquerels. Alternatively, the dosage may bemeasured by millicuries,for example. In some embodiments, the amount of¹⁸F imaging administered for imaging studies is 5 to 10 mCi. In otherembodiments, an effective amount will be the amount of compoundsufficient to produce emissions in the range of from about 1-5 mCi.

Actual dosage levels of the active ingredients in the pharmaceuticalcompositions described herein may be varied so as to obtain an amount ofthe active ingredient which is effective to achieve the desired uptakeof the ¹⁸F-labeled targeting agent in the cells or tissues of aparticular patient, composition, and mode of administration, withoutbeing toxic to the patient. It will be understood, however, that thetotal daily usage of the ¹⁸F-labeled targeting agent of the presentdisclosure will be decided by the attending physician or other attendingprofessional within the scope of sound medical judgment. The specificeffective dose level for any particular subject will depend upon avariety of factors, including for example, the activity of the specificcomposition employed; the specific composition employed; the age, bodyweight, general health, sex, and diet of the host; the time ofadministration; the route of administration; the rate of excretion ofthe specific compound employed; the duration of the treatment; otherdrugs, compounds and/or materials used in combination with theparticular compositions employed, the age, sex, weight, condition,general health and prior medical history of the patient being treated,and like factors well known in the medical arts. In certain embodiments,the amount of ¹⁸F-radiolabeled probe administered into a human subjectrequired for imaging will be determined by the prescribing physicianwith the dosage generally varying according to the quantity of emissionfrom the ¹⁸F-radionuclide.

A composition described herein can be administered via one or moreroutes of administration using one or more of a variety of methods knownin the art. As will be appreciated by the skilled artisan, the routeand/or mode of administration will vary depending upon the desiredresults. Preferred routes of administration for ¹⁸F-labeled targetingagent described herein include intravenous, intramuscular, intradermal,intraperitoneal, subcutaneous, spinal or other parenteral routes ofadministration, for example by injection or infusion. The phrase“parenteral administration” as used herein means modes of administrationother than enteral and topical administration, usually by injection, andincludes, without limitation, intravenous, intramuscular, intraarterial,intrathecal, intracapsular, intraorbital, intracardiac, intradermal,intraperitoneal, transtracheal, subcutaneous, subcuticular,intraarticular, subcapsular, subarachnoid, intraspinal, epidural andintrasternal injection and infusion. In certain embodiments,¹⁸F-radiolabeled targeting compound is administered intravenously.

Alternatively, an ¹⁸F-labeled targeting agent described herein can beadministered via a non-parenteral route, such as a topical, epidermal ormucosal route of administration, for example, intranasally, orally,vaginally, rectally, sublingually or topically.

In certain embodiments, the ¹⁸F-labeled targeting agent described hereincan be formulated to ensure proper distribution in vivo. For example,the blood-brain barrier (BBB) excludes many highly hydrophiliccompounds. Agents may cross the BBB by formulating them, for example, inliposomes. For methods of manufacturing liposomes, see, e.g., U.S. Pat.Nos. 4,522,811; 5,374,548; and 5,399,331. The liposomes may comprise oneor more moieties which are selectively transported into specific cellsor organs, thus enhance targeted drug delivery (see, e.g., V. V. Ranade(1989) J. Clin. Pharmacol. 29:685). Exemplary targeting moieties includefolate or biotin (see, e.g., U.S. Pat. No. 5,416,016 to Low et al.);mannosides (Umezawa et al., (1988) Biochem. Biophys. Res. Commun.153:1038); antibodies (P. G. Bloeman et al. (1995) FEBS Lett. 357:140;M. Owais et al. (1995) Antimicrob. Agents Chemother. 39:180); surfactantprotein A receptor (Briscoe et al. (1995) Am. J. Physiol. 1233:134);p120 (Schreier et al. (1994) J. Biol. Chem. 269:9090); see also K.Keinanen; M. L. Laukkanen (1994) FEBS Lett. 346:123; J. J. Killion; I.J. Fidler (1994).

The following illustrative procedure may be utilized when performing PETimaging studies on patients in the clinic. The patient is premedicatedwith unlabeled millamolecule some time prior to the day of theexperiment and is fasted for at least 12 hours allowing water intake adlibitum. A 20 G two-inch venous catheter is inserted into thecontralateral ulnar vein for radiotracer administration concentration inthe blood.

The patient is positioned in the PET camera and a tracer dose of the PETtracer of ¹⁸F-radiolabeled millamolecule (<20 mCi) is administered viai.v. catheter. Either arterial or venous blood samples are taken atappropriate time intervals throughout the PET scan in order to analyzeand quantitate the fraction of unmetabolized PET tracer of [¹⁸F] Example2 compound in plasma. Images are acquired for up to 120 min. Within tenminutes of the injection of radiotracer and at the end of the imagingsession, 1 ml blood samples are obtained for determining the plasmaconcentration of any unlabeled millamolecule which may have beenadministered before the PET tracer.

Tomographic images are obtained through image reconstruction. Fordetermining the distribution of radiotracer, regions of interest (ROIs)are drawn on the reconstructed image including, but not limited to, thelungs, liver, heart, kidney, skin or other organs and tissue.Radiotracer uptakes over time in these regions are used to generate timeactivity curves (TAC) obtained in the absence of any intervention or inthe presence of the unlabeled millamolecule at the various dosingparadigms examined. Data are expressed as radioactivity per unit timeper unit volume (μCi/cc/mCi injected dose). TAC data are processed withvarious methods well-known in the field to yield quantitativeparameters, such as Binding Potential (BP) or Volume of Distribution(V_(T)), that are proportional to the density of unoccupied targetpositive tissue.

Kits and Articles of Manufacture

Also provided are kits for producing the ¹⁸F-radiolabeled targetingcompositions described herein and instructions for use. Kits typicallyinclude a packaged combination of reagents in predetermined amounts withinstructions and a label indicating the intended use of the contents ofthe kit. The term label includes any writing, or recorded materialsupplied on or with the kit, or which otherwise accompanies the kit.

For example, in some embodiments, the kit contains the reagentsnecessary for the prosthetic group in condition to be fluorinated onsite with ¹⁸F, and then linking the radiolabeled prosthetic group to thetargeting molecule (e.g., millamolecule prior to administration.

In certain embodiments, a kit comprises one or more reagents necessaryfor forming an ¹⁸F labeled anti-PD-L1 millamolecule in vivo imagingagent, such as that described herein. For example, a kit may comprise afirst vial comprising anti-PD-L1 millamolecule and a second vialcomprising [¹⁸F]FPPEGA. A kit may comprise a first vial comprisinganti-PD-L1 millamolecule, a second vial comprising 4-PEG-tosyl-azide anda third vial comprising ¹⁸F in O¹⁸ water. The kits may further comprisevials, solutions and optionally additional reagents necessary for themanufacture of PD-L1 millamolecule-PEG4-DBCO-¹⁸F.

In some embodiments, the kit can further contain at least one additionalreagent (e.g., pharmaceutically acceptable carrier). In someembodiments, the kit includes the reaction precursors to be used togenerate the labeled probe according to the methods disclosed herein.The components of the kit can be tailored to the particular biologicalcondition to be monitored as described herein. The kit can furtherinclude appropriate buffers and reagents known in the art foradministering various combinations of the components listed above to thehost cell or host organism. The imaging agent and carrier may beprovided in solution or in lyophilized form. When the imaging agent andcarrier of the kit are in lyophilized form, the kit may optionallycontain a sterile and physiologically acceptable reconstitution mediumsuch as water, saline, buffered saline, and the like. Suitablecontainers include, for example, bottles, vials, syringes, and testtubes. The containers may be formed from a variety of materials such asglass or plastic. It may further include other materials desirable froma commercial and user standpoint, including other buffers, diluents,filters, needles, syringes, and package inserts with instructions foruse.

Uses

Methods of imaging using ¹⁸F-labeled targeting agents are providedherein. Positron emission tomography (PET) tracers such as the present¹⁸F-radiolabeled millamolecule-based PET probes can be used withcurrently available PET technology for use in exploratory and diagnosticimaging applications in vitro and in vivo. Imaging techniques andequipment for ¹⁸F imaging by PET scanning are well known in the art(see, e.g., U.S. Pat. Nos. 6,358,489; 6,953,567; Page et al., NuclearMedicine And Biology, 21:911-919, 1994; Choi et al., Cancer Research55:5323-5329, 1995; Zalutsky et al., J. Nuclear Med., 33:575-582, 1992)and any such known PET imaging technique or apparatus may be utilized.

In vivo applications of the imaging methods provided herein includedisease diagnosis, monitoring of disease progression, prognosis,determining likelihood of a subject to respond to a treatment,determining eligibility to a treatment, monitoring of clinical responseto therapy, clinical evaluation and dose selection of therapeuticcompounds, preclinical studies of potential drug candidates in animalmodels, and the study of regional distribution and concentration oftarget molecules in tissues and organs. In vitro applications includescreening of drug candidates in cell assays (e.g., competition assays,affinity assays, etc.).

In some embodiments, the ¹⁸F-labeled targeting agents can be used todetermine the relationship between level of tissue occupancy bycandidate therapeutic compounds and clinical efficacy in patients; todetermine dose selection for clinical trials of drug candidates prior toinitiation of long term clinical studies; and to compare potencies ofdifferent drug candidates.

In some embodiments, the ¹⁸F-radiolabeled targeting compound is used ina method for in in vivo imaging normal or diseased tissues and/or organs(e.g., lungs, heart, kidneys, liver, and skin). For example, the¹⁸F-radiolabeled targeting compound is administered to a subject in anamount effective to result in uptake of the ¹⁸F-radiolabeled targetingcompound into the cells or tissue of interest. The subject is thenintroduced to an appropriate imaging system (e.g., PET system) for asufficient amount of time to allow detection of the ¹⁸F-radiolabeledtargeting compound. The location of the detected signal from the¹⁸F-radiolabeled targeting compound can be correlated with the locationof the cells or tissue of interest. In some embodiments, the dimensionsof the location can be determined as well. In vivo imaging is describedherein. See also U.S. Pat. Nos. 6,126,916; 6,077,499; 6,010,680;5,776,095; 5,776,094; 5,776,093; 5,772,981; 5,753,206; 5,746,996;5,697,902; 5,328,679; 5,128,119; 5,101,827; and 4,735,210, eachincorporated herein by reference.

Accordingly, in certain aspects, provided is a method of obtaining animage of an ¹⁸F-radiolabeled millamolecule-based probe, the methodcomprising administering the ¹⁸F-radiolabeled millamolecule-based probeto a subject, and imaging in vivo the distribution of the¹⁸F-radiolabeled millamolecule-based probe by PET.

In certain embodiments, the subject is a mammal, for example, a human,dog, cat, ape, monkey, rat, or mouse.

In certain aspects, provided is a method of diagnosing the presence of adisease in a subject, the method comprising administering to a subjectin need thereof an ¹⁸F-radiolabeled millamolecule-based probe whichbinds to a target molecule associated with the presence of the disease,and obtaining a radio-image of at least a portion of the subject todetect the presence or absence of the ¹⁸F-radiolabeledmillamolecule-based probe.

In some embodiments, the disease is a solid cancer, hematopoieticcancer, hematological cancer, autoimmune disease, neurodegenerativedisease, cardiovascular disease or pathogenic infection.

PET imaging with an ⁸F-radiolabeled targeting compound may be used toqualitatively or quantitatively detect the targeting compound. An⁸F-radiolabeled targeting compound imaging agent may be used as abiomarker, and the presence or absence of a positive signal in a subjectmay be indicative that, e.g., the subject would be responsive to a giventherapy, e.g., a cancer therapy, or that the subject is responding ornot to a therapy.

In some embodiments, the steps of this method can be repeated atdetermined intervals so that the location and/or size of the disease canbe monitored as a function of time and/or treatment. In certainembodiments, the ¹⁸F-radiolabeled targeting compound can be used in asubject undergoing treatment (e.g., chemotherapy, etc.), to aid invisualizing response to the treatment. For example, the ¹⁸F-radiolabeledtargeting compound is typically visualized and sized prior to treatment,and periodically (e.g., daily, weekly, monthly, intervals in betweenthese, and the like) during treatment to monitor the progression orregression of the disease in the patient.

Accordingly, in certain aspects, provided is a method of monitoring theprogress of a disease in a subject in need thereof, the methodcomprising administering to the subject an ¹⁸F-radiolabeledmillamolecule-based probe which binds to a target molecule associatedwith the presence of the disease at a first time point and obtaining animage of at least a portion of the subject to determine the amount ofdiseased cells or tissue, and administering to the subject the¹⁸F-radiolabeled millamolecule-based probe at one or more subsequenttime points and obtaining an image of at least a portion of the subjectat each subsequent time point (e.g., same portion as the first timepoint).

In certain embodiments, the size of a tumor can be monitored in asubject undergoing cancer therapy (e.g., chemotherapy, radiotherapy) andthe extent of regression of the tumor can be monitored in real-timebased on detection of ¹⁸F-radiolabeled tumor targeting.

In some embodiments, the methods herein are used to evaluate thepatient's response to therapy. In some embodiments, the methods are usedto select or modify the dosage of therapeutic compounds. In someembodiments, the methods are used to monitor the uptake of the¹⁸F-radiolabeled targeting compound in normal tissues to analyzetoxicity or patient to patient variation. In some embodiments, themethods are used to monitor drug efficacy or to detect drug resistance.

In some embodiments, the radiolabeled compounds are administered tomammals, preferably humans, in a pharmaceutical composition, eitheralone or in combination with pharmaceutically acceptable carriers ordiluents according to standard pharmaceutical practice. Suchcompositions can be administered orally or parenterally, including theintravenous, intramuscular, intraperitoneal, subcutaneous, rectal andtopical routes of administration. In certain embodiments, administrationis intravenous. In certain embodiments the radiolabeled compound isadministered via intravenous injection within less than one hour ofsynthesis.

In some embodiments, the biological activity of the ¹⁸F-radiolabeledtargeting agent in vivo may be measured in terms of organ-specificuptake by biodistribution studies and dynamic small animal PET imagingstudies in an appropriate animal model. For example, for biodistributionstudies, a group of animals are injected with the ¹⁸F-radiolabeledtargeting agent and the subsets of the animals are sacrificed at one ormore time intervals (e.g., 5 min., 10 min., 30 min., 60 min., 2 h).Organs and tissues of interest are rapidly excised and weighed, andradioactivity determined. Accumulated radioactivity in organs andselected tissues is calculated as the percentage of injected dose (%ID).

In some embodiments, the ¹⁸F-radiolabeled targeting agent providedherein is used in vitro as a screening tool to select compounds for usein treating tissues or cells. For example, in some embodiments, diseasedcells are incubated with the ¹⁸F-radiolabeled targeting compound duringor after exposure to one or more candidate drugs. The ability of thedrug candidate to affect the disease can be imaged over time using the¹⁸F-radiolabeled targeting compound.

For example, the integrity of biological activity of the¹⁸F-radiolabeled targeting agent in vitro in terms of specific bindingto the selected target molecule and uptake of the radiolabeledcomposition is assessed in a cell line expressing the target molecule.For binding and cell association assays, cells are incubated at 4° C. or37° C. for an appropriate time with the ¹⁸F-radiolabeled targetingcomposition. Nonspecific binding is determined by the addition of anexcess of unlabeled targeting agent. The extent of specific binding iscalculated by subtracting the nonspecific binding from the totalbinding. Uptake is expressed as a percentage of the total added dose oftargeting agent to the cells per microgram of protein (% ID/μg cellprotein).

In a related aspect, the present invention provides a diagnostic orradiopharmaceutical composition for in vivo or in vitro, which includesan ¹⁸F-radiolabeled millamolecule-based probe, and a pharmaceuticallyacceptable carrier.

Incorporation by Reference

All documents and references, including patent documents and websites,described herein are individually incorporated by reference to into thisdocument to the same extent as if there were written in this document infull or in part.

The disclosure is now described by reference to the following examples,which are illustrative only, and are not intended to limit the presentdisclosure. While the disclosure has been described in detail and withreference to specific embodiments thereof, it will be apparent to one ofskill in the art that various changes and modifications can be madethereto without departing from the spirit and scope thereof.

Analysis Condition A

Column: Waters BEH C18, 2.0×50 mm, 1.7-μm particles; Mobile Phase A:5:95 acetonitrile:water with 10 mM ammonium acetate; Mobile Phase B:95:5 acetonitrile: water with 10 mM ammonium acetate; Temperature: 50°C.; Gradient: 0% B, 0-100% B over 3 minutes, then a 0.5-minute hold at100% B; Flow: 1 mL/min; Detection: UV at 220 nm.

Analysis Condition B

Column: Waters BEH C18, 2.0×50 mm, 1.7-μm particles; Mobile Phase A:5:95 methanol:water with 10 mM ammonium acetate; Mobile Phase B: 95:5methanol:water with 10 mM ammonium acetate; Temperature: 50° C.;Gradient: 0% B, 0-100% B over 3 minutes, then a 0.5-minute hold at 100%B; Flow: 0.5 mL/min; Detection: UV at 220 nm.

Single-Coupling Procedure

To the reaction vessel containing resin from the previous step was addedpiperidine:DMF (20:80 v/v, 5.0 mL). The mixture was periodicallyagitated for 3 or 5 min. and then the solution was drained through thefrit. To the reaction vessel was added piperidine:DMF (20:80 v/v, 5.0mL). The mixture was periodically agitated for 3 or 5 min. and then thesolution was drained through the frit. The resin was washed successivelyfive times as follows: for each wash, DMF (4.0 mL) was added through thetop of the vessel and the resulting mixture was periodically agitatedfor 60 seconds before the solution was drained through the frit. To thereaction vessel was added the amino acid (0.2M in DMF, 5.0 mL, 10 eq),then HATU or HCTU (0.2M in DMF, 5.0 mL, 10 eq), and finally NMM (0.8M inDMF, 2.5 mL, 20 eq). The mixture was periodically agitated for 60 min.,then the reaction solution was drained through the frit. The resin waswashed successively four times as follows: for each wash, DMF (4.0 mL)was added through the top of the vessel and the resulting mixture wasperiodically agitated for 30 seconds before the solution was drainedthrough the frit. To the reaction vessel was added a solution of aceticanhydride:DIEA:DMF (10:1:89 v/v/v, 5.0 mL). The mixture was periodicallyagitated for 10 min., then the solution was drained through the frit.The resin was washed successively four times as follows: for each wash,DMF (4.0 mL) was added through the top of the vessel and the resultingmixture was periodically agitated for 90 seconds before the solution wasdrained through the frit. The resulting resin was used directly in thenext step.

Double-Coupling Procedure

To the reaction vessel containing resin from the previous step was addeda solution of piperidine:DMF (20:80 v/v, 5.0 mL). The mixture wasperiodically agitated for 3 min. and then the solution was drainedthrough the frit. To the reaction vessel was added a solution ofpiperidine:DMF (20:80 v/v, 5.0 mL). The mixture was periodicallyagitated for 3 min. and then the solution was drained through the frit.The resin was washed successively three times as follows: DMF (7 mL)wash from top, followed by DMF (7 mL) wash from bottom and finally withDMF (7 mL) wash from top. To the reaction vessel was added the aminoacid (0.2M in DMF, 2.5 mL, 5 eq), HATU (0.5M in DMF, 1.0 mL, 5 eq), andDIPEA (2M in NMP, 0.5 mL, 10 eq). The mixture was mixed by N₂ bubblingfor 5 min. at 75° C. for all amino acids, except Fmoc-Cys(Trt)-OH andFmoc-His(Trt)-OH which are coupled at 50° C., the reaction solution wasdrained through the frit. The resin was washed successively three timesas follows: DMF (7 mL) wash from top, followed by DMF (7 mL) wash frombottom and finally with DMF (7 mL) wash from top. To the reaction vesselwas added the amino acid (0.2M in DMF,2.5 mL, 5 eq), HATU (0.5M in DMF,1.0 mL, 5 eq), and DIPEA (2M in NMP, 0.5 mL, 10 eq). The mixture wasmixed by N₂ bubbling for 5 min. at 75° C. for all amino acids, exceptFmoc-Cys(Trt)-OH and Fmoc-His(Trt)-OH which are coupled at 50° C., thereaction solution was drained through the frit. The resin was washedsuccessively three times as follows: DMF (7 mL) wash from top, followedby DMF (7 mL) wash from bottom and finally with DMF (7 mL) wash fromtop. To the reaction vessel was added a solution of aceticanhydride:DIEA:DMF (10:1:89 v/v/v, 5.0 mL). The mixture was periodicallybubbled for 2 min. at 65° C., then the solution was drained through thefrit. The resin was washed successively three times as follows: DMF (7mL) wash from top, followed by DMF (7 mL) wash from bottom and finallywith DMF (7 mL) wash from top. The resulting resin was used directly inthe next step.

The following peptide was synthesized on a 0.1 mmol. The underlinedsteps employed the double-coupling procedure, and italicized residueswere coupled with a 30 min single coupling.ClAc-Tyr-[N-Me]Ala-Asn-Pro-Dap-Leu-Hyp-Trp-Dab-[(S)-2-amino-3-(1-(carboxymethyl)-1H-indol-3-yl)propanoicacid]—[N-Me]Nle-[N-Me]Nle-Leu-Cys-Gly-[(S)-propargylglycine]; where the(S) propargylglycine was incorporated onto 2-chlorotrityl resin. Afterdeprotection and cyclization according to the procedures above, thecompound was purified as follows: The crude material was purified viapreparative LC/MS with the following conditions: Column: XBridge C18,19×200 mm, 5-μm particles; Mobile Phase A: 5:95 methanol: water with10-mM ammonium acetate; Mobile Phase B: 95:5 methanol: water with 10-mMammonium acetate; Gradient: 45-85% B over 30 minutes, then a 5-minutehold at 100% B; Flow: 20 mL/min. Fractions containing the desiredproduct were combined and dried via centrifugal evaporation. The yieldof the product was 16.4 mg, and its estimated purity by LCMS analysiswas 96%. Analysis condition A: Retention time=1.49 min; ESI-MS(+) m/z992.3 (M+2H), most abundant ion. Analysis condition B: Retentiontime=3.02 min; ESI-MS(+) m/z 992.3 (M+2H), most abundant ion;ESI-HRMS(+) m/z: Calculated: 991.9953 (M+2H)

Found: 991.9926 (M+2H).

Synthesis of[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine

EXAMPLE 1: PREPARATION OF 2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethyl4-methylbenzenesulfonate

A mixture of ((oxybis(ethane-2,1-diyl))bis(oxy))bis(ethane-2,1-diyl)bis(4-methylbenzenesulfonate) (5 g, 9.95 mmol) and sodium azide (0.647g, 9.95 mmol) were dissolved in ethanol (50 mL) and the reaction wasrefluxed at 90° C. over a 17 hour period. The solvent was removed usingpartial vacuum and then loaded onto a 40 gram silica cartridge andpurified using flash chromatography (IscoCombiFlash—eluted using alinear gradient method starting from 10% ethyl acetate in hexanes goingto a 90% ethyl acetate in hexanes over a 45 minute period). The pooledfractions were checked by TLC and combined to give2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethyl 4-methylbenzenesulfonate as acolorless oil. Due to the reactive nature of the2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethyl 4-methylbenzenesulfonateproduct this material was used “as is” without any furthercharacterizations.

EXAMPLE 2: PREPARATION OF3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine

To a suspension of sodium hydride (0.129 g, 3.21 mmol) in DMF (10 mL) at0° C. was dropwise added a stirring solution of 2-fluoropyridin-3-ol(0.363 g, 3.21 mmol) in DMF (5 mL), then followed by the dropwiseaddition of the solution of 2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethyl4-methylbenzenesulfonate (1.00 g, 2.68 mmol) in DMF (5 mL). Thesuspension was held at 0° C. for 10 min, then brought to ambienttemperature for 1 hour, followed by additional heating at 60° C. for 4hours. The solvent was removed in vacuo. 100 ml of ethyl acetate wasadded followed by 3 separate wash extractions with concentrated brinesolution. The organic layer was dried over sodium sulfate, filtered, andconcentrated. The crude material was purified using flash chromatography(IscoCombiFlash—eluted with 10-50% EtOAc in Hex) to give a colorlessoil. 3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine(702 mg, 2.233 mmol, 83% yield) was isolated as a clear oil. ¹H NMR (400MHz, CHLOROFORM-d) δ7.75 (dt, J=4.9, 1.6 Hz, 1H), 7.33 (ddd, J=10.0,8.1, 1.5 Hz, 1H), 7.10 (ddd, J=7.9, 4.9, 0.7 Hz, 1H), 4.30-4.16 (m, 2H),3.95-3.83 (m, 2H), 3.80-3.61 (m, 10H), 3.38 (t, J=5.1 Hz, 2H) 13C NMR(101 MHz, CHLOROFORM-d) d 142.3, 137.7, 137.5, 123.4, 123.4, 121.7,121.6, 77.3, 76.7, 70.9, 70.7, 70.6, 70.0, 69.4, 69.0, 50.6 19F NMR (400MHz, CHLOROFORM-d) δ−83.55. HRMS (ESI) Theory:C13H20FN4O4+ m/z 315.464;found 315.1463.

EXAMPLE 3: PREPARATION OF3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-nitropyridine

Sodium hydride (0.121 g, 3.01 mmol) (60% suspension in oil) wasdissolved in DMF (7.0 mL) and the resulting suspension was cooled to 0°C. A solution of 2-nitropyridin-3-ol (0.384 g, 2.74 mmol) in DMF (1.5mL) was added slowly, followed by the dropwise addition of2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethyl 4-methylbenzenesulfonate(1.023 g, 2.74 mmol) in DMF (1.5 mL). The suspension was held at 0° C.for 10 minutes, then brought to ambient temperature for 2 hours followedby heating 60° C. for a 72 hour period. The reaction was quenched with10 ml of DI water, followed by ethyl acetate extraction (3×10 mL).Pooled EtOAc extracts were washed with a concentrated brine solution (10mL), dried over sodium sulfate, filtered, and evaporated under reducedpressure to give a light yellow oil. The crude was purified by flashchromatography. 24 g silica cartridge, 25 mL/min, starting from 10%ethyl acetate in hexanes, followed by a linear change to 50% ethylacetate in hexanes over a 25 minute period. After this time, thegradient was held at this solvent composition for 10 minutes thenchanged to 100% ethyl acetate over a 10 minute period.3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-nitropyridine waseluted between the 30-40 minute portion of the chromatogram and thepooled fractions were evaporated under reduced pressure, then undervacuum for 2 hours to give3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-nitropyridine (687 mg,1.973 mmol, 72.0% yield) as a light yellow oil. ¹H NMR (400 MHz,CHLOROFORM-d) δ8.11 (dt, J=4.9, 1.6 Hz, 1H), 7.60 (ddd, J=10.0, 8.1, 1.5Hz, 1H), 7.52 (ddd, J=7.9, 4.9, 0.7 Hz, 1H), 4.30-4.16 (m, 2H),3.95-3.83 (m, 2H), 3.80-3.61 (m, 10H), 3.38 (t, J=5.1 Hz, 2H) 13C NMR(101MHz, CHLOROFORM-d) d 147.3, 139.5, 128.4, 124.4. 71.1, 70.7,70.6,70.0, 69.9, 69.3, 50.7. HRMS (ESI) Theory:C13H20N5O6+ m/z 342.1408;found 342.1409.

EXAMPLE 4: SYNTHESIS OF3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-bromopyridine

To the suspension of sodium hydride (NaH, 25.7 mg, 0.643 mmol) indimethylformamide (DMF, 5 mL) at 0° C. was dropwise added a solution of2-bromopyridin-3-ol (112 mg, 0.643 mmol) in DMF (1 mL), followed by thedropwise addition of the solution of2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethyl 4-methylbenzenesulfonate (200mg, 0.536 mmol) in DMF (1 mL). The suspension was held at 0° C. for 10minutes, then brought to ambient temperature and held for 1 hour,followed by heating to 60° C. for 4 hours. Upon completion of heating,the solvent of the crude reaction mixture was removed in vacuo. Thecrude reaction was reconstituted in 50 mL of ethyl acetate, washed with2×50 mL of a aqueous brine solution, and the organic layer was driedover magnesium sulfate, filtered, and concentrated in vacuo. The crudereaction was purified using reverse-phase HPLC to give3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-bromopyridine, TFA(112 mg, 0.229 mmol, 42.7% yield) as a light yellow oil. HRMS ESI m/z(M+H), Theory C13H20BrN4O4 375.0664 found 375.0662 ; ¹H NMR (400MHz,DMSO-d₆) δ7.97 (dd, J=4.6, 1.5 Hz, 1H), 7.54 (dd, J=8.2, 1.6 Hz, 1H),7.40 (dd, J=8.1, 4.6 Hz, 1H), 4.24 (dd, J=5.3, 3.9 Hz,2H), 3.85-3.78 (m,2H), 3.68-3.62 (m, 2H), 3.62-3.52 (m, 8H), 3.42-3.34 (m, 2H).

Synthesis of Trimethylanilium Compound

EXAMPLE 5 : SYNTHESIS OF3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N-dimethylpyridin-2-amine

A mixture of3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine (160mg, 0.509 mmol), potassium carbonate (K₂CO₃, 84 mg, 0.611 mmol), anddimethylamine (40% in water, 0.097 mL, 0.764 mmol) in dimethylsulfoxide(DMSO, 2.5 mL) were heated in a sealed pressure-proof vessel at 110° C.for 14 hours. Upon completion of heating, the solvent of the crudereaction mixture was removed in vacuo. The crude reaction wasreconstituted in 50 mL of ethyl acetate, washed with 2×50 mL of aaqueous brine solution, and the organic layer was dried over magnesiumsulfate, filtered, and concentrated in vacuo. The crude reaction waspurified using normal-phase chromatography to give3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N-dimethylpyridin-2-amine(140 mg, 0.413 mmol, 81% yield) as a colorless oil. ¹H NMR (400 MHz,CHLOROFORM-d) δ7.86 (dd, J=4.9, 1.5 Hz, 1H), 7.02 (dd, J=7.8, 1.5 Hz,1H), 6.73 (dd, J=7.8, 4.9 Hz, 1H), 4.20-4.07 (m, 2H), 3.98-3.86 (m, 2H),3.81-3.61 (m, 9H), 3.38 (t, J=5.1 Hz, 2H), 3.13-2.94 (m, 6H), 1.69 (s,2H). HRMS (ESI) Theory:C15H26N5O4+ m/z 340.1980; found 340.1979.

EXAMPLE 6 : SYNTHESIS OF3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N,N-trimethylpyridin-2-aminium

Methyl trifluoromethanesufonate (0.065 mL, 0.589 mmol) was added to thesolution of3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N-dimethylpyridin-2-amine(40 mg, 0.118 mmol) in toluene (1.5 mL) in a sealed container under asteady stream of nitrogen. The reaction mixture was stirred at roomtemperature over a 14 hour period. The solvent was removed and theresultant residue was washed with 2×10 ml of ether, azeotropically driedwith 2×1 ml of dichloromethane, and dried under high-pressure vacuumovernight to give3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N,N-trimethylpyridin-2-aminium,trifluoromethanesulfonate salt in quantitative yield as a thickcolorless oil.

LCMS m/z 354.33; ¹H NMR (400 MHz, DMSO-d₆) δ8.24-8.17 (m, 1H), 7.98 (d,J=8.3 Hz, 1H), 7.75 (ddd, J=8.2, 4.6, 3.2 Hz, 1H), 4.44 (br. s., 2H),3.88 (d, J=3.9 Hz, 2H), 3.69-3.45 (m, 21H).

EXAMPLE 7: SYNTHESIS OF[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridineUSING3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N,N-trimethylpyridin-2-aminium,trifluoromethanesulfonate salt

An aqueous [¹⁸F]-Fluoride solution (2.0 ml, 33.3 GBq/900 mCi) waspurchased from P.E.T. Net° Pharmaceuticals in West Point Pa. anddirectly transferred to a Sep-Pak light QMA [The Sep-Pak light QMAcartridge was pre-conditioned sequentially with 5 ml of 0.5 M potassiumbicarbonate, 5 ml of deionized water, and 5 ml of MeCN before use.] Uponcompletion of this transfer, the aqueous [¹⁸F] fluoride was releasedfrom the QMA Sep-Pak by the sequential addition of potassium carbonate(15 mg/ml; 0.1 ml) followed by a mixture of potassium carbonate (30mg/ml, 0.1 ml),4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (15 mg, 0.04mmol) and 1.2 ml of MeCN. The solvent was evaporated under a gentlestream of nitrogen at 90° C. and vacuum. Azeotropic drying was repeatedtwice with 1 ml portions of acetonitrile to generate the anhydrousK.2.2.2/K[¹⁸F]F complex.3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-N,N,N-trimethylpyridin-2-aminium,trifluoromethanesulfonate salt (2 mg, 5.6 μmol) was dissolved in 500microliters of DMSO and added to the dried cryptand. This solution washeated at 120° C. for 10 minutes. After this time, the crude reactionmixture was diluted with 3 ml of DI water. The entire contents of thecrude reaction mixture was then transferred, loaded, and purified usingreverse phase HPLC under the following conditions: HPLC Column: Luna C18250×10 Solvent A: 0.1% TFA in DI water; solvent B: 0.1% TFA inacetonitrile at a flow rate of 4.6 ml/minute using isocratic method 32%B while the UV was monitored at 280 nm.[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinewas isolated at the 24 min mark of the chromatogram and collect over a 2minute period. This product was collected into a 100 ml flask thatcontained 10 ml of DI water and the entire contents were delivered to aSep-Pak Vac tC18 6 cc 1 g sep pack from Waters. 6.1 GBq/164 mCi of[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinewas isolated from this reaction. This was released from the sep-pakusing 3 ml of ethanol and this solution was reduced with 98° C. heatsource, a gentle stream of nitrogen, and vacuum over a 15 minute perioduntil only a film remained in the vial. The final product wasreconstituted in 100% 1× PBS buffer and was stable in this media forover 1 hour at 37° C.

The[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinemay be used to generate ¹⁸F-labeled products (e.g., ¹⁸F-labeledanti-PD-L1 macrocyclic peptides, as described below) by taking advantageof “click” azide-alkyne reaction with the appropriate peptidescontaining an alkynes.

EXAMPLE 8: PRODUCTION OF ¹⁸F-RADIOLABELED MACROCYCLIC PEPTIDE USING“CLICK CHEMISTRY” A. Fluorination of the 4-PEG-tosyl-azide Precursor toform[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine

An aqueous [¹⁸F]-Fluoride solution (2.0 ml, 29.6 GBq/800 mCi) waspurchased from IBA in Towada and shipped to the BMS Princeton N.J. siteand this sample was transferred within our custom made remote controlledsynthesis. This solution was delivered to a Sep-Pak light QMA [TheSep-Pak light QMA cartridge was pre-conditioned sequentially with 5ml of0.5 M potassium bicarbonate, 5 ml of deionized water, and 5 ml of MeCNbefore use.] Upon completion of this transfer, the aqueous [¹⁸F]fluoride was released from the QMA Sep-Pak by the addition of a mixtureof potassium carbonate (30 mg/ml in distilled water (DI), 0.1 ml),4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (15 mg, 0.04mmol) and 1.4 ml of acetonitrile. The solvent was evaporated under agentle stream of nitrogen at 90° C. and vacuum. Azeotropic drying wasrepeated twice with 1 ml portions of acetonitrile to generate theanhydrous K.2.2.2/K[¹⁸F]F complex. Upon completion of this process thecryptand was further dried under full vacuum for a 15 minute period. Theentire process took 35 minutes to complete.

To this dried [¹⁸F]/cryptand solid was added 0.5 ml of 2 mg of3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-nitropyridine in DMSOand this mixture was heated at 120° C. for 10 minutes. After this timethe crude reaction mixture was diluted with 3 ml of distilled water andthe entire contents were then transferred and loaded onto the followingHPLC column and conditions: HPLC Column: Luna C18 250×10 mm; Solvent A:0.1% trifluoroacetic acid (TFA) in DI water; Solvent B: 0.1% TFA inacetonitrile; flow rate 4.6 ml/min; pressure 1820 PSI; isocratic method32% B; UV—280 nm. The[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridine([¹⁸F]-FPPEGA) product was isolated at the 24 minute mark of thechromatogram and was collected over a 2 minute period. This product wascollected into a 100 ml flask that contained 15 ml of DI water and theentire contents were delivered to a Sep PakVac tC18 6 cc 1 g sep pack(PN WAT036795). The [¹⁸F]-FPPEGA was released from the Sep Pak using 2.5ml of ethanol and this solution was reduced with 98° C. N₂ and vacuumover a 15 minute period until dryness. This compound was dissolved in0.1 ml DI water. This product was analysed using a Varian HPLC HPLCColumn Luna C18 (2) 4.6×150 mm Solvent A: 0.1% TFA in DI water; SolventB: 0.1% TFA in acetonitrile; flow rate 1.0 ml/min; gradient method 0 min90% A 10% B; 15 mins 30% A 70% B; 17 mins 30% A 70% B; 18 mins 90% A 10%B; 20 mins 90% A 10% B; UV—280 nm. 14.1 GBq (380 mCi) of [¹⁸F]-FPPEGAwas isolated. This product was carried forward to complete the “click”chemistry with alkyne containing PD-L1 binding macrocyclic peptide.

B. Coupling of [¹⁸F]-FPPEGA to macrocyclic peptide

A schematic for synthesizing [¹⁸F]-radiolabeled macrocyclic peptide isshown in Figure (a)

(S)-2-(2-((6S,9S,12S,18R,21S,24S,27S,30S,33S,36S,38aS,40R,44R,47S,49aS)-36-((1H-indol-3-yl)methyl)-6-(2-amino-2-oxoethyl)-33-(2-aminoethyl)-47-(aminomethyl)-24,27-dibutyl-30-((1-(carboxymethyl)-1H-indol-3-yl)methyl)-40-hydroxy-12-(4-hydroxybenzyl)-21,44-diisobutyl-9,10,25,28-tetramethyl-5,8,11,14,20,23,26,29,32,35,38,43,46,49-tetradecaoxohexatetracontahydro-1H,5H-dipyrrolo[2,1-g1:2′,1′-x][1]thia[4,7,10,13,16,19,22,25,31,34,37,40,43]tridecaazacyclopentatetracontine-18-carboxamido)acetamido)pent-4-ynoicacid (0.75 mg, 0.378 □mol) was dissolved in 0.250 ml of DI water and0.25 ml of tert-butyl alcohol. To this solution was added a 0.250 ml DIwater solution containg 1 mg cupric sulfate and 1 mg of sodiumascorbate. Finally, the 0.1 ml solution of 14 .1 GBq (380 mCi) of[¹⁸F]-FPPEGA (prepared as described in section A) was added and thereaction was gently mixed at ambient temperature for 20 minutes. To thecontents of this crude reaction mixture was added a 0.5 ml ofacetonitrile followed by 1.5 ml of DI water and this mixture waspurified using a reverse phase HPLC column. HPLC Column: Luna C18 250×10mm; Solvent A: 0.1% trifluoroacetic acid (TFA) in DI water; Solvent B:0.1% TFA in acetonitrile; flow rate 4.6 ml/min; pressure 1820 PSI;isocratic method 37% B; UV—220 nm. The product was isolated between the27-31 minute mark of the chromatogram and was collected over a 4 minuteperiod as shown in figure (b). 2.5 GBq (67 mCi) of[¹⁸F]-(S)-2-(2-((6S,9S,12S,18R,21S,24S,27S,30S,33S,36S,38aS,40R,44S,47S,49aS)-36-((1H-indol-3-yl)methyl)-6-(2-amino-2-oxoethyl)-33-(2-aminoethyl)-47-(aminomethyl)-24,27-dibutyl-30-((1-(carboxymethyl)-1H-indol-3-yl)methyl)-40-hydroxy-12-(4-hydroxybenzyl)-21,44-diisobutyl-9,10,25,28-tetramethyl-5,8,11,14,20,23,26,29,32,35,38,43,46,49-tetradecaoxohexatetracontahydro-1H,5H-dipyrrolo[2,1-g1:2′,1′-x][1]thia[4,7,10,13,16,19,22,25,28,31,34,37,40,43]tetradecaazacyclopentatetracontine-18-carboxamido)acetamido)-3-(1-(2-(2-(2-(2-((2-fluoropyridin-3-yl)oxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)propanoicacid was isolated. This solution was further diluted with 20 ml of DIwater and this solution was transferred to a C-18 sep-pak (Waters 50 mg,that was pre-activated with 5 ml of ethanol, followed by 10 ml of DIwater) to remove any organic solvent from the solution. This sep-pak wasfurther washed with 10 ml of sterile water for injection. This productwas released from the sep-pak with 0.5 ml of ethanol, sterile filteredinto a sterile vial and diluted to a 5% ethanol by volume solution withsaline for injection. This product was analyzed via reverse phase HPLCfor as shown in figure (b): chemical identify with co-injection ofnon-radioactive standard, radiochemical purity and chemical purity,specific activity. The isolated product co-eluted with non-radioactivereference standard, was 100% radiochemically and 95% chemically pure,with a specific activity of 0.37 (10 mCi) GBq/nmol.

Analytical reverse phase HPLC was performed with the followingparameters: Zorbax SB-C18 250×4.6 mm column; Solvent A: 0.05% formicacid in DI water; Solvent B: 0.05% in acetonitrile; flow rate 1.0ml/min; gradient method 30% to 50% B over 20 minutes; UV—220 nm.

Figure (a)

A schematic for synthesizing [¹⁸F]-radiolabeled PD-L1 bindingmacrocyclic peptide

The of[¹⁸F]-(S)-2-(2-((6S,9S,12S,18R,21S,24S,27S,30S,33S,36S,38aS,40R,44S,47S,49aS)-36-((1H-indol-3-yl)methyl)-6-(2-amino-2-oxoethyl)-33-(2-aminoethyl)-47-(aminomethyl)-24,27-dibutyl-30-((1-(carboxymethyl)-1H-indol-3-yl)methyl)-40-hydroxy-12-(4-hydroxybenzyl)-21,44-diisobutyl-9,10,25,28-tetramethyl-5,8,11,14,20,23,26,29,32,35,38,43,46,49-tetradecaoxohexatetracontahydro-1H,5H-dipyrrolo[2,1-g1:2′,1′-x][1]thia[4,7,10,13,16,19,22,25,28,31,34,37,40,43]tetradecaazacyclopentatetracontine-18-carboxamido)acetamido)-3-(1-(2-(2-(2-(2-((2-fluoropyridin-3-yl)oxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)propanoicacid can be used in a variety of in vitro and/or in vivo imagingapplications, including diagnostic imaging, basic research, andradiotherapeutic applications. Specific examples of possible diagnosticimaging and radiotherapeutic applications, include determining thelocation, the relative activity and/or quantifying of PD-L1 positivetumors, radioimmunoassay of PD-L1 positive tumors, and autoradiographyto determine the distribution of PD-L1 positive tumors in a mammal or anorgan or tissue sample thereof.In particular, the[¹⁸F]-(S)-2-(2-((6S,9S,12S,18R,21S,24S,27S,30S,33S,36S,38aS,40R,44S,47S,49aS)-36-((1H-indol-3-yl)methyl)-6-(2-amino-2-oxoethyl)-33-(2-aminoethyl)-47-(aminomethyl)-24,27-dibutyl-30-((1-(carboxymethyl)-1H-indol-3-yl)methyl)-40-hydroxy-12-(4-hydroxybenzyl)-21,44-diisobutyl-9,10,25,28-tetramethyl-5,8,11,14,20,23,26,29,32,35,38,43,46,49-tetradecaoxohexatetracontahydro-1H,5H-dipyrrolo[2,1-g1:2′,1′-x][1]thia[4,7,10,13,16,19,22,25,28,31,34,37,40,43]tetradecaazacyclopentatetracontine-18-carboxamido)acetamido)-3-(1-(2-(2-(2-(2-((2-fluoropyridin-3-yl)oxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)propanoicacid is useful for positron emission tomographic (PET) imaging of PD-L1positive tumors in the lung, heart, kidneys, liver and skin and otherorgans of humans and experimental animals.PET imaging using the[¹⁸F]-(S)-2-(2-((6S,9S,12S,18R,21S,24S,27S,30S,33S,36S,38aS,40R,44S,47S,49aS)-36-((1H-indol-3-yl)methyl)-6-(2-amino-2-oxoethyl)-33-(2-aminoethyl)-47-(aminomethyl)-24,27-dibutyl-30-((1-(carboxymethyl)-1H-indol-3-yl)methyl)-40-hydroxy-12-(4-hydroxybenzyl)-21,44-diisobutyl-9,10,25,28-tetramethyl-5,8,11,14,20,23,26,29,32,35,38,43,46,49-tetradecaoxohexatetracontahydro-1H,5H-dipyrrolo[2,1-g1:2′,1′-x][1]thia[4,7,10,13,16,19,22,25,28,31,34,37,40,43]tetradecaazacyclopentatetracontine-18-carboxamido)acetamido)-3-(1-(2-(2-(2-(2-((2-fluoropyridin-3-yl)oxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)propanoicacid can be used to obtain the following information: relationshipbetween level of tissue occupancy by candidate PD-L1 tumor-treatingmedicaments and clinical efficacy in patients; dose selection forclinical trials of PD-L1 tumor-treating medicaments prior to initiationof long term clinical studies; comparative potencies of structurallynovel PD-L1 tumor-treating medicaments; investigating the influence ofPD-L1 tumor-treating medicaments on in vivo transporter affinity anddensity during the treatment of clinical targets with PD-L1tumor-treating medicaments; changes in the density and distribution ofPD-L1 positive tumors during effective and ineffective treatment.

EXAMPLE 9: AUTOMATED PREPARATION OF[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridineACCORDING TO THE GENERAL PROCEDURE FOR THE SYNTHESIS RADIOSYNTHESIS ONGE TRACERlab FX2 N SYNTHESIS UNIT

Automated Synthesis Using Commercial TRACERlab FX2 N Synthesis Module(GE)

The automated synthesis of[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinewas carried out using a non-cassette type GE TRACERlab FX2 N Synthesismodule. The setup of the synthesis unit is summarized in Table ( ). Theaqueous [¹⁸F]-Fluoride solution (2.0 ml, 29.6 GBq/800 mCi) was deliveredto a Sep-Pak light QMA [The Sep-Pak light QMA cartridge waspre-conditioned sequentially with 5 ml of 0.5 M potassium bicarbonate, 5ml of deionized water, and 5 ml of acetonitrile before use.] Uponcompletion of this transfer, the aqueous [¹⁸F] fluoride was releasedfrom the QMA Sep-Pak by the addition of a the elution mixture (from“V1”) into the reactor. The solvent was evaporated under a gentle streamof nitrogen and vacuum. The solution of precursor (from “V3”) was addedto the dried cryptand residue and this reaction mixture was heated 120°C. for 10 minutes. Then 4 ml of distilled water (from “V4”) was added tothe crude reaction mixture in the reactor and the mixture is transferredto the 5 ml sample injection loop of the semi-preparative HPLC via aliquid sensor which controls the end of the loading. The mixture isloaded onto the semi-preparative HPLC column ( Luna C18(2). 250×10 mm,Phenomenex). A mixture of 35% acetonitrile in an aqueous 0.1%trifluoroacetic acid solution was flushed through the column at a rateof 4.6 ml per minute. The product was collected from this HPLC columninto the dilution flask which contained 15 ml distilled water and itsentire contents were transferred to a tC18 1 gram, solid phaseextraction cartridge. 352 mCi (13 GBq) of[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinewas released from this cartridge ( from “V14”) with 3 ml of ethanol andmay be used to generate ¹⁸F labeled peptide products by taking advantageof “click” azide-alkyne reaction with the appropriate peptide containingan alkynes.

TABLE 1 Vial 1 (V1) 16 mg K.2.2.2, 3 mg Potassium carbonate, dissolvedin 0.1 ml of distilled water and 1.4 ml of acetonitrile Vial 3 (V3) 2 mg3-(2-(2-(2-(2- azidoethoxy)ethoxy)ethoxy)ethoxy)-2- nitropyridine in 0.5ml DMSO Vial 4 (V4) 4 ml of distilled water Vial 14 (V14) 3 ml of 100%ethanol Dilution Flask 15 ml of distilled water Cartridge 1 (C1) tC18 6cc 1 g sep pack HPLC Column Luna C18(2), 250 × 10 mm, 5 □m, PhenomenexHPLC Solvent 35% acetonitrile in an aqueous 0.1% trifluoroacetitic acidsolution HPLC flow 4.6 ml/min

EXAMPLE 10: AUTOMATED PREPARATION OF[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridineACCORDING TO THE GENERAL PROCEDURE FOR THE SYNTHESIS RADIOSYNTHESIS ONIBA Synthera SYNTHESIS UNIT

Automated Synthesis Using Commercial Synthera Synthesis Module (IBA)

The automated synthesis of[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinewas carried out using a cassette type IBA Synthera Synthesis module andan appropriately assembled integrator fluidic processor kit. Theintegrator fluidic processor (IFP) kit was loaded with appropriateprecursors for this synthesis and is summarized in Table ( ). Thepurification was performed on an Varian HPLC unit. The filling of theinjection loop of the HPLC was controlled by a steady stream of nitrogenon the HPLC unit. The setup of both automates are summarized in Table (). The aqueous [¹⁸F]-Fluoride solution (2.0 ml, 29.6 GBq/800 mCi) wasdelivered to a Sep-Pak light QMA [The Sep-Pak light QMA cartridge waspre-conditioned sequentially with 5 ml of 0.5 M potassium bicarbonate, 5ml of deionized water, and 5 ml of acetonitrile before use.]. Uponcompletion of this transfer, the aqueous [¹⁸F] fluoride was releasedfrom the QMA Sep-Pak by the addition of a the elution mixture (from“V1”) into the reactor. The solvent was evaporated under a gentle streamof nitrogen and vacuum. The solution of precursor (from “V2”) was addedto the dried cryptand residue and this reaction mixture was heated 120°C. for 10 minutes. Then 3 ml of distilled water (from “V4”) was added tothe crude reaction mixture in the reactor and the mixture is transferredto the 5 ml sample injection loop of the semi-preparative HPLC via aliquid sensor which controls the end of the loading. The mixture isloaded onto the semi-preparative HPLC column ( Luna C18(2). 250×10 mm,Phenomenex). A mixture of 35% acetonitrile in an aqueous 0.1%trifluoroacetic acid solution was flushed through the column at a rateof 4.6 ml per minute. The product was collected from this HPLC columninto the dilution flask which contained 15 ml distilled water and itsentire contents were transferred to a tC18 1 gram, solid phaseextraction cartridge. 325 mCi (12 GBq) of[¹⁸F]-3-(2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)ethoxy)-2-fluoropyridinewas released from this cartridge with 3 ml of ethanol and may be used togenerate ¹⁸F labeled peptide products by taking advantage of “click”azide-alkyne reaction with the appropriate peptide containing analkynes.

TABLE 2 Vial 1 (V1) 22 mg K.2.2.2, 4 mg Potassium carbonate, dissolvedin 0.3 ml of distilled water and 0.3 ml of acetonitrile Vial 2 (V2) 2 mg3-(2-(2-(2-(2- azidoethoxy)ethoxy)ethoxy)ethoxy)-2- nitropyridine in 0.5ml DMSO Vial 4 (V4) 3 ml of distilled water Dilution Flask 15 ml ofdistilled water Cartridge 1 (C1) tC18 6 cc 1 g sep pack HPLC Column LunaC18(2), 250 × 10 mm, 5 □m, Phenomenex HPLC Solvent 35% acetonitrile inan aqueous 0.1% trifluoroacetitic acid solution HPLC flow 4.6 ml/min

EXAMPLE 11: DISTINGUISHING PD-L1-POSITIVE TUMORS FROM PD-L1-NEGATIVETUMORS WITH AN ANTI-PD-L1 MACROCYCLIC PEPTIDE IMAGING AGENT

For PET imaging, rapid blood clearance rates provide an advantage overmore slowly clearing agents, such as antibodies, by minimizing theamount of time needed for “background” probe signals to deplete fromnon-relevant tissue. In the clinic, long blood half-lifeantibody-based-PET tracers may require several days of waiting postinjection before images can be collected. Rapid clearing probes open thedoor to high contrast images that can be collected on the same day theprobe is injected, and very importantly, they can also serve to reduceoverall radiation exposure to the animals studied or patients examined.

In this experiment, the [¹⁸F]labelled macrocyclic PD-L1 peptide wasproduced as described in the above Examples, was tested for its abilityto discriminate between hPD-L1-positive tumors and hPD-L1-negativetumors in mice.

Mice bearing bilateral xenograft tumors were produced by introducing2×10⁶ hPD-L1(+) L2987 human lung carcinoma cells and 4×10⁶ hPD-L1(−)HT-29 human colon carcinoma cells subcutaneously on opposite sides ofthe mouse. Once tumors reached approximately 300 mm³ (approximately 2-3weeks after cell implantation), animals were selected for imaging. Thebody weight and tumor size of each study were measured and recorded onthe imaging day before imaging procedure. Mice were placed in ananesthetic induction chamber and 3% isoflurane inhalant anesthesia wasdelivered in 100% O₂ at a rate of 1-1.5 L/min. Once sedated, mice wereremoved from the induction chamber and placed into a plexiglass4-chamber mouse hotel (custom-made by BMS-Applied Biotechnology group),while continuing to receive 1-1.5% isoflurane inhalant anesthesia anddelivered in 100% O₂ at a rate of 2 L/min via the nose-cone. Animal werekept warm using an external standalone temperature regulating unit (M2MImaging Corp) to prevent hypothermia during imaging. Mouse respirationwas continuously monitored during imaging procedures and isoflurane maybe adjusted dependent on depth of anesthesia. Mice were then placed intoa custom animal holder with capacity for 4 animals, where they remainedunder anesthesia for the duration of the study. The animal holder wastransferred to the microPET® F120™ scanner (Siemens PreclinicalSolutions, Knoxville, Tenn.). The axial field of view of this instrumentis 7.6 cm. With this limitation, animals were positioned such that thescanning region was from immediately in front of the eyes toapproximately the base of the tail. A 10-minute transmission image wasfirst acquired using a ⁵⁷Co point source for the purpose of attenuationcorrection of the final PET images. Following the transmission scan,radiotracer solutions were administered via the previously installedtail vein catheters and a 2 hour emission image was acquired. Injectedradiotracer solutions were injected into a total 8 mice (body weight:22.2±2.0 gram) with tumor volumes 203.0±51.4 mm³ for HT-29 and422.9±128.4 mm³ for L2987 were imaged 16-17 days post cell implantation.Each mouse received a single injection of SC dose of PD-L1 bindingmacrocyclic peptide 60 mg/kg (N=4) or saline (N=4) 30 minute before the[¹⁸F]labelled macrocyclic PD-L1 peptide (124.0±8.4 μCi, tracer mass:1.0±0.4 μg/kg) IV injection. Images were reconstructed using a maxiumuma posteriori (MAP) algorithm with attenuation correction using thecollected transmission images and corrected for radioisotope decay. Inthe final images, regions of interest (ROIs) were drawn around the tumorboundary using ASIPro software (Siemens Preclinical Solutions).Time-activity curves were calculated for each ROI to yield aquantitative view of radiotracer within the tumor volume over the courseof the 2 hour emission image. For final comparison, individualtime-activity curves were normalized based on the injected radiotracerdose for each specific animal. Radiotracer uptake was compared acrosstumors using the final 10 minutes of each time-activity curve (90-100minutes post-radiotracer injection). Using this methodology, radiotraceruptake in hPD-L1(+) L2987 xenografts was 8.1 × that seen hPD-L1(−) HT-29xenografts in animals receiving only the [¹⁸F]labelled macrocyclic PD-L1peptide radiotracer. In animals receiving SC dose of PD-L1 bindingmacrocyclic peptide 60 mg/kg 30 minutes before the radiotracerinjection. Uptake in the hPD-L1(+) L2987 xenografts was only 0.7 × thatseen in hPD-L1(−) HT-29 xenografts (FIG. 1, FIG. 2 and Table 3).

TABLE 3 The standard uptake values (SUV) in HT-29 and L2987 tumorsderived from PET images in Example 11 PD-L1 binding Body Volume ofVolume of Injected Tracer macrocyclic Mouse weight HT-29 L2987 dose massSUV in SUV in peptide # (gram) (mm³) (mm³) (μCi) (μg/kg) HT29 L2987 0mg/kg Mouse 3 20.4 180 500 132.6 4.60 0.036 0.213 (Saline) Mouse 7 21.3144 320 110.9 4.63 0.033 0.231 Mouse 19 24.4 162 245 100.5 1.45 0.0470.452 Mouse 23 22.1 87.5 126 81.7 1.66 0.031 0.297 Mean 22.1 143.4 297.8106.4 3.1 0.037 0.298 (Stdev) (1.7) (40.0) (156.7) (21.2) (1.8) (0.007)(0.109) 60 mg/kg Mouse 6 23.0 64 171.5 114.4 4.36 0.102 0.060 Mouse 1222.0 126 288 90.5 4.58 0.084 0.055 Mouse 22 23 126 760.5 71.3 1.41 0.0300.042 Mouse 28 23.8 108 320 118.1 2.63 0.065 0.043 Mean 23.0 106.0 385.098.6 3.2 0.071 0.050 (Stdev) (0.7) (29.3) (258.3) (21.9) (1.5) (0.031)(0.009)

These results provide direct visualization of differentiation ofhPD-L1(+) vs. hPD-L1(−) xenograft tumors in vivo. Specificity wasfurther demonstrated by predosing PD-L1 binding macrocyclic peptide 60mg/kg 30 minutes before the radiotracer injection, resulting in areduction of radiotracer uptake in hPD-L1(+) tumors to the level ofhPD-L1(−) xenografts. This further validates the use of PD-L1macrocyclic peptides for visualization of PD-L1 tissue expression usingPET imaging.

EXAMPLE 12: PET IMAGING IN NON-HUMAN PRIMATE WITH AN ANTI-PD-L1MACROCYCLIC PEPTIDE IMAGING AGENT

The anti-PD-L1 millamolecule-based imaging agents also showed similarresults when performed in cynomolgus monkeys. In these studies, the[¹⁸F]labelled macrocyclic PD-L1 peptide, produced as described in theabove Examples, was tested for its ability to produce high-contrastimages in cynomolgus monkeys. The anti-PD-L1 macrocyclic peptidesdescribed here maintain high affinity for cynomolgus PD-L1 (but have lowaffinity for rodent PD-L1). Furthermore, as cynomolgus monkeys do notcontain PD-L1(+) tumors as in mouse models, imaging performance wasassessed primarily on the background levels measured in the images inthe context of endogenous PD-L1 expression (with low background enablingthe potential for high-sensitivity detection of PD-L1(+) tissues). Inthese studies, background levels in the resulting PET images were verylow, with notable radiotracer accumulation noted mainly in the kidneys,spleen, and bladder.

Cynomolgus male monkeys with a previously installed vascular access port(VAP) were anesthetized with 0.02 mg/kg atropine, 5 mg/kg Telazol and0.01 mg/kg buprenorphine I.M. (all drawn into a single syringe). An i.v.catheter is then placed in the cephalic vessel for fluid administrationduring the imaging procedure to maintain hydration. Animals wereintubated with an endotracheal tube—usually 3.0 mm and transferred tothe imaging bed of a microPET® F220™ PET instrument (Siemens PreclinicalSolutions, Knoxville, Tenn.). Anesthesia was maintained with isofluraneand oxygen and I.V. fluids (LRS) were administered at a rate of 6ml/kg/hr during the imaging procedure. As the axial field of view of themicroPET® F220™ instrument is only 7.6 cm, images over 5 distinct bedpositions were acquired to create a composite image of the animals fromjust above the heart through approximately the pelvis.

For each field of view, a 10 minute transmission image was firstacquired using a ⁵⁷Co point source for the purpose of attenuationcorrection of the final PET images. Once transmission images wereacquired for all bed positions, approximately 1.7 mCi (approximately0.12 μg/kg) of the [¹⁸F]labelled macrocyclic PD-L1 peptide radiotracerwas administered via the installed VAP. 5 minute duration emission scanswere then sequentially acquired for each bed position, beginning atposition 1 centered approximately at the heart and moving toward thepelvis of the animal. Once images were acquired at each position (1through 5), the imaging bed was moved back to bed position 1 and theprocess was repeated. Using this procedure, a total of 5 distinct imageswere acquired for each bed position over the duration of the imagingstudy.

Individual images were reconstructed using a filtered back projection(FBP) algorithm with attenuation correction using the collectedtransmission images and corrected for radioisotope decay. Finalcomposite images were then produced by aligning images from all 5 bedpositions obtained from a single pass (i.e. a single composite image wasproduced from each set of sequential images from bed positions 1 through5) covering the duration of the imaging study. Final images werevisually inspected to note areas of visible radiotracer uptake (i.e.spleen, liver, kidney) and background tissue (muscle) (FIG. 3).Background accumulation of the [¹⁸F]labelled macrocyclic PD-L1 peptideradiotracer was very low, with little signal visible in backgroundtissues such as muscle. Additionally, uptake was verified in the spleen,which is PD-L1(+) based on immuno-histochemistry and mRNA expression.Thus, studies in cynomolgus monkeys demonstrate the potential forhigh-sensitivity PD-L1 imaging in the context of endogenous PD-L1. Todetermine the nature of the specific binding in the cynomolgus monkeyspleen a blocking study was conducted in the following manner.

The cynomolgus monkey (4.4 kg, male) received a single IV injection of[¹⁸F]labelled macrocyclic PD-L1 peptide radiotracer (˜1.7 mCi, mass:0.21 μg/kg) at baseline. On the following day (post-dose), the same NHPreceived a single SC dose of 2 mg/kg anti-PD-L1 binding macrocyclicpeptide at 2 hours before radiotracer injection (˜1.7 mCi, mass: 0.12μg/kg). The tracer uptake in various organs are listed in Table 4.Representative PET images of baseline and post-dose are plotted in FIG.3. The plasma concentrations of the anti-PD-L1 binding macrocyclicpeptide were measured at 0, 10, 30, 60, 90 minutes after radiotracerinjection on each imaging day (Table 4). A specific binding signal wasobserved within the spleen of the non-human primate with 93% of traceruptake was blocked with 2 mg/kg of a specific PD-L1 binding macrocyclicpeptide.

PET studies in rodent and cynomolgus monkey show that ¹⁸F labeledanti-human PD-L1 macrocyclic peptide provide strong and specific probesfor in vivo labeling of PD-L1 positive tissues with the potential forhigh-sensitivity detection of tissues with low level PD-L1 expression.

In vivo imaging experiments were also conducted with an anti-PD-L1antibody, and the areas that this imaging agent detected were the sameareas that were detected with the PD-L1 imaging agent, thereforeconfirming that anti-PD-L1 millamolecule imaging agents successfullydetect PD-L1 positive cells in vivo.

TABLE 4 Tracer SUV in each organ in baseline and post-dose with 2 mg/kgPD-L1binding macrocyclic peptide. Blocked with 2 mg/kg of PD-L1 bindingSUV Baseline macrocyclic peptide % Change Spleen 19.720 1.423 −92.8%Kidney Pelvis 8.855 24.061 171.7% Kidney Cortex 8.420 10.846 28.8%Duodenum 8.840 8.756 −0.9% Liver 9.163 3.165 −65.5% Gallbladder 2.7761.128 −59.4% Lung 1.856 0.793 −57.3% Muscle 0.521 0.341 −34.7% Thymus1.992 0.931 −53.3% * % change = (SUV in before − SUV in after)/SUV inbefore

EXAMPLE 13: IN VITRO AUTORADIOGRAPHY WITH [¹⁸F]LABELLED MACROCYCLICPD-L1 PEPTIDE RADIOTRACER

Human lung tumor tissues were embedded in OCT and chilled in2-methylbutane for 2-5 minutes until frozen. Samples were stored in −80°C. degree freezer until use. Human xenograft tissues were also includedin the assay. Mice bearing bilateral xenografts were produced byintroducing 2×10⁶ hPD-L1(+) L2987 human lung carcinoma cells and 4×10⁶hPD-L1(−) HT-29 human colon carcinoma cells subcutaneously on oppositesides of the mouse. Once resulting xenograft tumors reached appropriatesize (approx. 200-300 mm³), mice were anesthetized with 2% isofluraneand sacrificed via cervical dislocation. Fresh tumor tissues wereexcised, immersed into OCT and chilled in 2-methylbutane for 2-5 minutesuntil frozen. The tissues were then wrapped in foil/ZIPLOC® bag andstored at −80° C. until use. For all tissues (human lung tumor andxenografts) sections of 5 μm thickness (collected as 2 sections/slide)were cut using a cryostat, thaw-mounted on glass microscope slides, andallowed to air dry for approximately 30 minutes. Blocking studies withcold (unlabelled) peptide at 0.1 nM, 1 nM, and 10 nM respectively. Theindividual slides, 1 slide per concentration, were transferred to glassslide incubation chambers for incubation. Separately, a stock solutionof 0.25 nM[¹⁸F]-(S)-2-(2-((6S,9S,12S,18R,21S,24S,27S,30S,33S,36S,38aS,40R,44S,47S,49aS)-36-((1H-indol-3-yl)methyl)-6-(2-amino-2-oxoethyl)-33-(2-aminoethyl)-47-(aminomethyl)-24,27-dibutyl-30-((1-(carboxymethyl)-1H-indol-3-yl)methyl)-40-hydroxy-12-(4-hydroxybenzyl)-21,44-diisobutyl-9,10,25,28-tetramethyl-5,8,11,14,20,23,26,29,32,35,38,43,46,49-tetradecaoxohexatetracontahydro-1H,5H-dipyrrolo[2,1-g1:2′,1′-x][1]thia[4,7,10,13,16,19,22,25,28,31,34,37,40,43]tetradecaazacyclopentatetracontine-18-carboxamido)acetamido)-3-(1-(2-(2-(2-(2-((2-fluoropyridin-3-yl)oxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)propanoicacid was produced by diluting 10.6 μl of the original stock radioligandsolution (7064 nM at the time of experiment) with 300 ml of tween 80.From this stock solution, 40 ml was added to each incubation chamber.One of these chambers contained only the radioligand buffer solution,which is referred to as the total binding section. Other incubationchambers received 40 ml of this stock solution along with the relevantconcentration of blocking compound (unlabelled peptide at 0.1 nM, 1 nM,or 10 nM). Slides were incubated in the individual buffer solutions for1 hour at room temperature to reach maximum binding. After incubation,slides from each treatment group were removed from the incubationsolutions and placed in an ice-cold wash buffer (Tween 80) for 3 minutesand rinsed 4 separate times. Slides were then dried under a stream ofcold air for approximately 30 minutes. The air-dried slides were exposedby placing the slides onto an imaging plate (BAS-SR 3545S) overnight atroom temperature. The imaging plate was scanned using the bioimaginganalyzer (Fujifilm Fluorescent Image Analyzer, FLA-9000). The pixel sizeof the autoradiogram images was 100 μm. Image analysis was performedusing the Multi-Gauge software. The regions of interest (ROIs) weredrawn to surround the entire tumor tissue in all study groups.Autoradiography signals from tissue-associated radioactivity werequantified from these ROIs. The apparent displacement of the[¹⁸F]labelled macrocyclic PD-L1 peptide radiotracer when compared to thetotal binding sections was determined for 3 different concentrations(0.1 nM, 1 nM, and 10 nM) of unlabeled peptide in both human lung tumorsections as well as human xenograft sections. A dose dependentdisplacement of [¹⁸F]labelled macrocyclic PD-L1 peptide radiotracer wasseen in all tissue sections with the addition of unlabelled peptide(FIG. 4). Serial 5 μm tissue sections from each tissue were subjected toan anti-human-PD-L1 immunohistochemical procedure to verify the level ofPD-L1 antigen expression in the samples confirmed PD-L1 expression inhuman lung samples.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents of the specificembodiments described herein. Such equivalents are intended to beencompassed by the following claims.

What is claimed is:
 1. A compound of formula (I)

or a pharmaceutically acceptable salt thereof, wherein x is an integer from 1 to 8 and R is a C₁-C₆alkyl group.
 2. A compound of claim 1 of formula (II)

or a pharmaceutically acceptable salt thereof, wherein x is an integer from 1 to 8 and R is C₁-C₆alkyl group.
 3. A compound of claim 1 of formula (III)

or a pharmaceutically acceptable salt thereof.
 4. A compound of formula (IV)

or a pharmaceutically acceptable salt thereof, wherein x is an integer from 1 to 8 and R is C₁-C₆alkyl group.
 5. A compound of claim 4 of formula (V)

or a pharmaceutically acceptable salt thereof.
 6. A method of obtaining an image of a compound of claim 1, the method comprising, a) administering the compound to a subject; and b) imaging in vivo the distribution of the compound positron emission tomography (PET) scanning.
 7. The method of claim 6, wherein the imaged distribution of the compound of claim 1 is indicative of the presence or absence of a disease.
 8. A method of monitoring the progress of a disease in a subject, the method comprising (a) administering to a subject in need thereof a compound of claim 1 which binds to a target molecule associated with the presence of the disease at a first time point and obtaining an image of at least a portion of the subject to determine the amount of the diseased cells or tissue; and (b) administering to the subject compound of claim 1 at one or more subsequent time points and obtaining an image of at least a portion of the subject at each time point; wherein the dimension and location of the diseased cells or tissue at each time point is indicative of the progress of the disease.
 9. A method of quantifying diseased cells or tissues in a subject, the method comprising (a) administering to a subject having diseased cells or tissues a compound of claim 1 which binds to a target molecule located with the diseased cells or tissues; and (b) detecting radioactive emissions of the ¹⁸F in the diseased cells or tissue, wherein the level and distribution of the radioactive emissions in the diseased cells or tissues is a quantitative measure of the diseased cells or tissues.
 10. The method of claim 9 wherein the disease is selected from the group consisting of solid cancers, hematopoietic cancers, hematological cancers, autoimmune disease, neurodegenerative disease cardiovascular disease, and pathogenic infection.
 11. A method of obtaining a quantitative image of tissues or cells expressing PD-L1, the method comprising contacting the cells or tissue with a compound of claim 1 which binds to PD-L1, and detecting or quantifying the tissue expressing PD-L1 using positron emission tomography (PET).
 12. A method of screening for an agent for treating a disease comprising the steps of (a) contacting cells expressing PD-L1 with a compound of claim 1 which binds to PD-L1 in the presence and absence of a candidate agent; and (b) imaging the cells in the presence and absence of the candidate agent using positron emission tomography (PET), wherein a decrease in the amount of radioactive emissions in the presence of the candidate agent is indicative of that the agent binds to PD-L1.
 13. A pharmaceutical composition comprising a compound of claim
 1. 14. A kit comprising the reaction precursors for use in producing the compound of claiml, and instructions for producing the compound of claim
 1. 